Prevent excessive DB load due to faulty DeleteConflictingRedirectRoutesRange background migration

What does this MR do?

Mitigate any more potential damage to GitLab.com and customers from DeleteConflictingRedirectRoutesRange background jobs all running at the same time and timing out.

See https://gitlab.com/gitlab-com/infrastructure/issues/3460#note_53223252

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

What are the relevant issue numbers?

https://gitlab.com/gitlab-com/infrastructure/issues/3460