[App] Add support for plugins to return actions

[ethanwharris]

What does this PR do?

• Allows a plugin to return actions that show a toast message or navigate to a page.
• Refactors LightningPlugin to live in lightning.app.plugin

Before submitting

• Was this discussed/agreed via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

Anyone in the community is welcome to review the PR.
Before you start reviewing, make sure you have read the review guidelines. In short, see the following bullet-list:

Reviewer checklist

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cc @Borda

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 lightning_app: Tests workflow

Check ID	Status
app-pytest (macOS-11, lightning, 3.8, latest)	success	✅
app-pytest (macOS-11, lightning, 3.8, oldest)	success	✅
app-pytest (macOS-11, app, 3.9, latest)	success	✅
app-pytest (ubuntu-20.04, lightning, 3.8, latest)	success	✅
app-pytest (ubuntu-20.04, lightning, 3.8, oldest)	success	✅
app-pytest (ubuntu-20.04, app, 3.9, latest)	success	✅
app-pytest (windows-2022, lightning, 3.8, latest)	success	✅
app-pytest (windows-2022, lightning, 3.8, oldest)	success	✅
app-pytest (windows-2022, app, 3.8, latest)	success	✅

These checks are required after the changes to src/lightning/app/__init__.py, src/lightning/app/core/__init__.py, src/lightning/app/plugin/__init__.py, src/lightning/app/plugin/actions.py, src/lightning/app/plugin/plugin.py, src/lightning/app/runners/cloud.py, src/lightning/app/utilities/cloud.py, src/lightning/app/utilities/load_app.py, tests/tests_app/plugin/__init__.py, tests/tests_app/plugin/test_plugin.py, tests/tests_app/runners/test_cloud.py, requirements/app/base.txt.

🟢 lightning_app: Examples

Check ID	Status
app-examples (macOS-11, lightning, 3.9, latest)	success	✅
app-examples (macOS-11, lightning, 3.9, oldest)	success	✅
app-examples (macOS-11, app, 3.9, latest)	success	✅
app-examples (ubuntu-20.04, lightning, 3.9, latest)	success	✅
app-examples (ubuntu-20.04, lightning, 3.9, oldest)	success	✅
app-examples (ubuntu-20.04, app, 3.9, latest)	success	✅
app-examples (windows-2022, lightning, 3.9, latest)	success	✅
app-examples (windows-2022, lightning, 3.9, oldest)	success	✅
app-examples (windows-2022, app, 3.9, latest)	success	✅

These checks are required after the changes to src/lightning/app/__init__.py, src/lightning/app/core/__init__.py, src/lightning/app/plugin/__init__.py, src/lightning/app/plugin/actions.py, src/lightning/app/plugin/plugin.py, src/lightning/app/runners/cloud.py, src/lightning/app/utilities/cloud.py, src/lightning/app/utilities/load_app.py, requirements/app/base.txt.

🟢 lightning_app: Azure

Check ID	Status
App.cloud-e2e	success	✅

These checks are required after the changes to src/lightning/app/__init__.py, src/lightning/app/core/__init__.py, src/lightning/app/plugin/__init__.py, src/lightning/app/plugin/actions.py, src/lightning/app/plugin/plugin.py, src/lightning/app/runners/cloud.py, src/lightning/app/utilities/cloud.py, src/lightning/app/utilities/load_app.py, requirements/app/base.txt.

🟢 lightning_app: Docs

Check ID	Status
make-doctest (lightning)	success	✅
make-html (lightning)	success	✅

These checks are required after the changes to src/lightning/app/__init__.py, src/lightning/app/core/__init__.py, src/lightning/app/plugin/__init__.py, src/lightning/app/plugin/actions.py, src/lightning/app/plugin/plugin.py, src/lightning/app/runners/cloud.py, src/lightning/app/utilities/cloud.py, src/lightning/app/utilities/load_app.py, requirements/app/base.txt.

🟢 mypy

Check ID	Status
mypy	success	✅

These checks are required after the changes to requirements/app/base.txt, src/lightning/app/__init__.py, src/lightning/app/core/__init__.py, src/lightning/app/plugin/__init__.py, src/lightning/app/plugin/actions.py, src/lightning/app/plugin/plugin.py, src/lightning/app/runners/cloud.py, src/lightning/app/utilities/cloud.py, src/lightning/app/utilities/load_app.py.

🟢 install

Check ID	Status
install-pkg (ubuntu-22.04, app, 3.8)	success	✅
install-pkg (ubuntu-22.04, app, 3.10)	success	✅
install-pkg (ubuntu-22.04, fabric, 3.8)	success	✅
install-pkg (ubuntu-22.04, fabric, 3.10)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.8)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.10)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.8)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.10)	success	✅
install-pkg (ubuntu-22.04, notset, 3.8)	success	✅
install-pkg (ubuntu-22.04, notset, 3.10)	success	✅
install-pkg (macOS-12, app, 3.8)	success	✅
install-pkg (macOS-12, app, 3.10)	success	✅
install-pkg (macOS-12, fabric, 3.8)	success	✅
install-pkg (macOS-12, fabric, 3.10)	success	✅
install-pkg (macOS-12, pytorch, 3.8)	success	✅
install-pkg (macOS-12, pytorch, 3.10)	success	✅
install-pkg (macOS-12, lightning, 3.8)	success	✅
install-pkg (macOS-12, lightning, 3.10)	success	✅
install-pkg (macOS-12, notset, 3.8)	success	✅
install-pkg (macOS-12, notset, 3.10)	success	✅
install-pkg (windows-2022, app, 3.8)	success	✅
install-pkg (windows-2022, app, 3.10)	success	✅
install-pkg (windows-2022, fabric, 3.8)	success	✅
install-pkg (windows-2022, fabric, 3.10)	success	✅
install-pkg (windows-2022, pytorch, 3.8)	success	✅
install-pkg (windows-2022, pytorch, 3.10)	success	✅
install-pkg (windows-2022, lightning, 3.8)	success	✅
install-pkg (windows-2022, lightning, 3.10)	success	✅
install-pkg (windows-2022, notset, 3.8)	success	✅
install-pkg (windows-2022, notset, 3.10)	success	✅

These checks are required after the changes to src/lightning/app/__init__.py, src/lightning/app/core/__init__.py, src/lightning/app/plugin/__init__.py, src/lightning/app/plugin/actions.py, src/lightning/app/plugin/plugin.py, src/lightning/app/runners/cloud.py, src/lightning/app/utilities/cloud.py, src/lightning/app/utilities/load_app.py, requirements/app/base.txt.

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Thank you for your contribution! 💜

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[awaelchli]

@ethanwharris I think the tests/__init__.py was added by accident. I think it should be removed, this could be the cause of the import errors in the tests.

[tchaton]

LGMT !

[carmocca]

I created a PR for the 1.9.4 release. @ethanwharris Can you cherry-pick the changes from this PR into #16884?

[carmocca]

Should this have a CHANGELOG entry?

[ethanwharris]

@carmocca No, not user facing at this time 😃