Use Gitaly 0.52.1 in 10-2-stable

What does this MR do?

Bumps the Gitaly version in 10-2-stable to 0.52.1. We intentionally target 10-2-stable, not master, because master has Gitaly 0.55.0 already and we don't want to downgrade there.

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

Why was this MR needed?

We are having performance issues with Gitaly on gitlab.com since the first 10-2-stable deploy. This new Gitaly version adds Go pprof support, which should help us analyze what Gitaly is spending its CPU and RAM on in production.

We cut the 0.52.1 Gitaly release specifically for this purpose; it has no other change besides adding pprof.

https://gitlab.com/gitlab-org/gitaly/blob/0-52-stable/CHANGELOG.md

Screenshots (if relevant)

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?