Switch to mypy part1

[m-vdb]

Proposed changes:
Fix the following typing issues:

• dict-item
• list-item
• call-arg

Leftovers to merge this PR

• this discussion in rasa.core.actions.action to resolve (needs input from reviewer)
• this discussion in rasa.core.actions.two_stage_fallback to resolve (needs input from reviewer)
• this discussion in rasa.core.test to resolve (ready to implement)
• this discussion in rasa.shared.nlu.training_data.lookup_tables_parser to resolve (ready to implement)
• this discussion on tests to resolve (needs input from reviewer)
• API spec to update (see rasa.server module)
• merge main in the branch and fix merge conflicts
• Update rasa.model.Fingerprint typing (possibly in another task)

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)

[m-vdb]

@wochinge after merging master into this branch, I have to fix more issues. I have a question about ActionExecuted. Is it safe to assume that it should only be initialised with action_name and/or action_text, but if both are None, then we should raise an error?

[wochinge]

All done besides from a small snippet in rasa.server.

Nice work! Cool to see that mypy also helps us detecting and removing technical debt! 🥇

[m-vdb]

@wochinge thanks for your review! This PR was not really ready for review, but the "part0" is. Would you mind taking a look?

[wochinge]

🙈 will do

[wochinge]

Nice to get this in! 🚀 Great work! Do we have follow up issues for the enable squad for this?

[m-vdb]

@wochinge no we don't as I don't know how the squad wants to split the work on this yet. Maybe let's have a single placeholder issue to discuss this, and create other issues when we're ready to tackle it?

[wochinge]

Do you have some up do date statistics how often each error type is occuring? How about putting this in the squad channel? In my opinion we should have ready to go issue for refinement and then sprint planning.

[m-vdb]

let me compile this and share it