[Rails5] Add `touch_later` to `Commit` model

What does this MR do?

This MR adds the touch_later method to the Commit model which fixes errors like:

1) API::Todos GET /todos when unauthenticated returns authentication error
    Failure/Error: @raw.__send__(method, *args, &block) # rubocop:disable GitlabSecurity/PublicSend
    
    NoMethodError:
      undefined method `touch_later' for #<Gitlab::Git::Commit:0x00005573f5196270>
    # ./app/models/commit.rb:259:in `method_missing'
    # ./spec/requests/api/todos_spec.rb:12:in `block (2 levels) in <top (required)>'

Are there points in the code the reviewer needs to double check?

No.

Why was this MR needed?

Migration to Rails 5.0

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#14286 (closed) and !12841 (closed)