Improve how Renovate groups NodeJS PRs

[noahtallen]

Proposed Changes

Renovate opens too many PRs for NodeJS. For example:

• Random engines field: chore(deps): update node.js to >=v14.21.3 - autoclosed #80522
• Another random engines field: chore(deps): update node.js to ^v16.20.1 - autoclosed #80523
• Most Node things: chore(deps): update dependency @types/node to ^18.17.3 - autoclosed #80345
• CircleCI: chore(deps): update node.js to v18.17.1 - autoclosed #80649

On top of that, Renovate doesn't update a few other version constants in the repo, like GitHub actions.

To fix:

• Attempt to group the CircleCi update in with the main Node PR
• Attempt to exclude one package.json file from node updates, since it should stay low
• Remove the engines field from the generator package; it isn't needed.
• Use nvmrc for setup-node in GH actions, since it's supported.
• Remove some cases where we hardcoded the Node version in readmes; it doesn't seem worth keeping these updates when we can just reference the nvmrc or engines field.
• Use regex to update one of the Docker images

Testing Instructions

See if Renovate combines these PRs.

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-77556

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-77556&env=jetpack

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[noahtallen]

The changes here are working a lot better -- everything is combined into this PR now: #80658. I think parts aren't quite working (like the one engines field I don't want it to update), but I'll keep looking at that as a follow-up.