feat: add backups_sync management command

[nijel]

Proposed changes

Checklist

• Lint and unit tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added documentation to describe my feature.
• I have squashed my commits into logic units.
• I have described the changes in the commit messages.

Other information

[codecov]

Codecov Report

Attention: Patch coverage is 11.47541% with 54 lines in your changes missing coverage. Please review.

Project coverage is 79.35%. Comparing base (8cd3876) to head (c64b430).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2364      +/-   ##
==========================================
- Coverage   80.28%   79.35%   -0.93%     
==========================================
  Files          51       52       +1     
  Lines        4438     4496      +58     
  Branches      425      435      +10     
==========================================
+ Hits         3563     3568       +5     
- Misses        726      779      +53     
  Partials      149      149