Resolve "[Rails5] Bump Rails5 to 5.0.7"

What does this MR do?

1. Updates Gemfile to use Rails 5.0.7 for rails5 (was 5.0.6).
2. Sets atomic gem to 1.1.99 because the current 1.1.100 version was yanked.

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)

No.

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?

Closes #46234 (closed)

#14286 (closed) and !12841 (closed)