Upgrade to Rails 7

[jazairi]

Why these changes are being introduced:

We want to stay up to date with the latest Rails.

Relevant ticket(s):

https://mitlibraries.atlassian.net/browse/ENGX-155

How this addresses that need:

This upgrades to Rails 7 and loads the new framework defaults.
Prior to this, I ran rails app:update, checked the diffs for all
files, and confirmed that the new framework defaults would not
cause problems. In this case, it seemed like there were no Rails
files that needed to be updated, so I kept the existing files.

Side effects of this change:

• The way we handle domain redirects
  (ApplicationController#ensure_domain) now throws an unsafe
  redirect error. I've added the allow_other_host param to that
  method to bypass this. In this case the other host would come
  from env, so the risk seems low, but I'd encourage the reviewer
  to consider any edge cases I may have missed.
• The only new framework default that seemed like it could cause
  problems for us was the key generator digest changing to SHA256:
  https://guides.rubyonrails.org/v7.0/upgrading_ruby_on_rails.html#key-generator-digest-class-changing-to-use-sha256.
  However, I don't think we are using encrypted cookies
  in this app, so I don't anticipate problems there.

Developer

• All new ENV is documented in README
• All new ENV has been added to Heroku Pipeline, Staging and Prod
• ANDI or Wave has been run in accordance to
  our guide and
  all issues introduced by these changes have been resolved or opened as new
  issues (link to those issues in the Pull Request details above)
• Stakeholder approval has been confirmed (or is not needed)

Code Reviewer

• The commit message is clear and follows our guidelines
  (not just this pull request message)
• There are appropriate tests covering any new functionality
• The documentation has been updated or is unnecessary
• The changes have been verified
• New dependencies are appropriate or there were no changes

Requires database migrations?

NO

Includes new or updated dependencies?

YES

[JPrevost]

Would you mind checking if we already have a ticket to update the dockerfile and if not creating one? It looks more out of date than the scope of this work so I'm not asking for it to be included here, but I think a TIMX ticket to update the various docker bits for this would be good if we don't have one yet.

I think this is the first major rails upgrade that didn't require deprecation cleanup... I'm betting some of our other apps won't be so clean :)

[jazairi]

Thanks, @JPrevost. I opened that ticket here: https://mitlibraries.atlassian.net/browse/TIMX-86