DEV: Add `annotate` rake tasks, and enforce via GitHub actions (PR #13636)

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The title of this pull request changed from “DEV: Add github actions script to check model annotations” to "DEV: Add annotate rake tasks, and enforce via GitHub actions

Nice! I think eventually we’ll make it so that it auto-commits any corrections.

Yeah I’d love to make it auto-commit. Problem is, I don’t think we can do that for PRs from forks (because the GITHUB_TOKEN isn’t provided in that case). But still, it could be useful for team PRs :+1: