WIP: Lower the max number of Gitaly calls

What does this MR do?

Lowers the maximum number of Gitaly calls permitted by the N+1 detector.

This is the first step proposed by @jacobvosmaer-gitlab:

I wonder if we could get more mileage out of the gitaly n+1 detector. It currently fails tests that do more than 30 gitaly calls. That is a very high number. We could try to gradually get that down to 10.

The general approach would be:

1. lower the limit in a MR
2. find out which tests fail in CI
3. place GitalyClient.allow_n_plus_1_calls blocks around code that makes too many gitaly calls
4. merge MR
5. then one by one get rid of the allow_n_plus_1_calls blocks

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/57911

gitaly#1504

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
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• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer