Update session cookie key name to be unique to instance in development

What does this MR do?

• Update session cookie key name to be unique to instance in development, _gitlab_session_dd3e97794060e2134ec763a0bb3dc6d3bbd011b33ea084ef272498a06c6b80b3
  • Generates hash from Rails.root, thanks @DouweM

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

Why was this MR needed?

When working with CE and EE on localhost, signing in to one, invalidates the other because they both overwrite the _gitlab_session cookie.

@MadLittleMods, https://gitlab.com/gitlab-org/gitlab-ce/issues/31644

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #31644 (closed)