Resolve "CE remote_mirrors table should have boolean enabled set to `false`"

What does this MR do?

This MR adds in a missing DB migration that changes the default for remote_mirrors.enabled from true to false.

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

Not sure if this is the correct way to port an EE DB migration back into CE.

Why was this MR needed?

When merging CE into EE, there was a db/schema.rb conflict which was caused by the missing DB migration.

Screenshots (if relevant)

N/A

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 #46130 (closed)