AO3-6605 Add Reviewdog for Rubocop check

[brianjaustin]

Pull Request Checklist

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• Have you read the contributing guidelines?
• Have you added tests for any changed functionality?
• Have you added the Jira issue number
  as the first thing in your pull request title (e.g. AO3-1234 Fix thing)
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Issue

https://otwarchive.atlassian.net/browse/AO3-6605

Purpose

Add a Reviewdog action to run Rubocop. This will give us more flexibility to add custom cops and upgrade to the latest version of rubcop (and its plugins). Example of how Rubocop warnings will show up: https://github.com/brianjaustin/ao3-sandbox/pull/1/files (the specific message is from a custom cop).

Note: no changes in what Rubocop flags are expected yet. Custom cops (and maybe other plugins?) will come in later PR(s)

Follow-Up Instructions

1. Allow-list the action in this Github repository's settings (similar to AO3-6590 Add reviewdog for linting ERB files #4604)
   2. Deactivate/remove this repository from our Hound account -- optional but recommended to avoid duplicate comments and errors when we upgrade or add custom cops

Credit

Brian Austin (they/he)

[Bilka2]

Deactivate/remove this repository from our Hound account -- optional but recommended

According to .hound.yml, Hound should be running jshint. This leaves the question whether it runs as configured or if, like ERB Lint, it doesn't actually run. But in any case, .hound.yml should be updated to disable rubocop.

[brianjaustin]

@Bilka2 good point! I have gotten JShint checks on a PR in the past, so I think it still works (at least somewhat)? I will also update the instructions to not totally remove Hound yet

[Bilka2]

Looks good and works on my fork. The suggested change would be nice to have though.

[redsummernight]

I've added reviewdog/action-rubocop@e70b014b8062c447d6b515ee0209f834ea93e696, to the repo setting "Allow specified actions and reusable workflows".