Add support for get_patch_id

What does this MR do and why?

We've added patch-id RPC in gitaly!5174 (merged) and now this MR provides an interface to call that RPC from rails side.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #406521 (closed)