Install RuboCop Rails to actually run RuboCop in CI

[bencomp]

I noticed that the "Run RuboCop" step in CI is always skipped, because RuboCop is not in the Gemfile(.lock). This PR adds RuboCop and RuboCop Rails. I followed https://github.com/rubocop/rubocop-rails#rubocop-configuration-file to add the .rubocop.yml file, although there is more to configure, as the output of RuboCop shows in https://github.com/bencomp/fromthepage/actions/runs/11937781469/job/33274542417.

[WillNigel23]

We are in the process of upgrading rails at the moment. That includes getting rubocop as part of the CI process.

The updates done here will only do warning for syntax. We plan to get to this sometime after the rails upgrade (as there are syntax changes too that are different from older versions I believe). For now I think we should leave it as is.

[bencomp]

Thanks for reviewing! However, I'm not sure I understand your comments.

RuboCop is already defined as a step in the CI process, i.e. the GitHub workflow. Currently it always fails because it isn't installed in the CI environment. This step is allowed to fail, so every time it runs, it produces an ignored error.
By default RuboCop runs as a linter that flags problems, without trying to fix them. In CI that is a good thing. Since there are very many violations of code style currently, it is probably a good thing to allow the RuboCop step to keep failing.
In this sense I'm leaving it as is.

I understand that Ruby 3 syntax is slightly different, but I don't think that matters here. As far as I can tell, RuboCop is smart and understands the version that you are using. I don't think this PR gets in the way of upgrading Rails.

Perhaps it is friendlier to contributors to eventually only run RuboCop on the code that they change/add in a PR, after deciding what (style) rules you want people to adhere to. Perhaps there are smarter ways of running RuboCop too, like running it with Reviewdog in a separate job.