Bump Gitaly server version to 0.5.0

Gitaly v0.5.0 includes the server implementation for Post(Upload|Receive)Pack calls. Client implementation has already landed in workhorse, bumping the version ties everything together.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together