Downgrade the grpc gem to 1.4.5

What does this MR do?

Downgrade the gRPC Ruby gem used by GitalyClient from 1.7.2 to 1.4.5.

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

Why was this MR needed?

It seems that gRPC 1.6.0 introduced a bug where clients (Ruby processes) can get in a state where they can no longer make RPC calls and report "call dropped" errors. This happens intermittently but regularly in production. Downgrading to 1.4.x is a desperate move to get rid of these errors that we have not been able to reproduce.

In the upstream issue https://github.com/grpc/grpc/issues/12506 a lot of people reported that downgrading solved the problem for them so that's why we want to do that too now.

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?

gitaly#810 (closed)