Rename PrimaryOrBackup

[marcellorigotti]

Pull Request

Closes: PRO-1554

Checklist

Please conduct a thorough self-review before opening the PR.

• [x] I am confident that the code works.
• [x] I have written sufficient tests.
• [x] I have written and tested required migrations.
• [x] I have updated documentation where appropriate.

Summary

• Renamed Secondary to Backup
• Added PrimaryOrBackup to the logs when a request fails

Non-Breaking changes

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 89.65517% with 6 lines in your changes missing coverage. Please review.

Project coverage is 71%. Comparing base (270839f) to head (0f3fb6d).

Files	Patch %	Lines
engine/src/retrier.rs	90%	3 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5139 +/- ## ===================================== Coverage 71% 71% ===================================== Files 460 460 Lines 81655 81655 Branches 81655 81655 ===================================== + Hits 58111 58116 +5 + Misses 20445 20444 -1 + Partials 3099 3095 -4 ```

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