Draft: Use moved GitLab client from Gitaly

See gitaly!3850 (closed).

Looking at the number of dependencies:

• Current main has 406 dependencies.
• If we pull in the latest version of Gitaly, the number is 472.
• This branch allows us to drop this number to 459.

➜  gitlab-shell git:(main) ✗ go list -m all | wc -l                                                          
     406
➜  gitlab-shell git:(main) ✗ go get gitlab.com/gitlab-org/gitaly/v14@master                                  
go get: upgraded gitlab.com/gitlab-org/gitaly/v14 v14.0.0-rc1 => v14.3.0-rc1.0.20210909083229-4534c1b11dfc
go get: upgraded golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad => v0.0.0-20210506145944-38f3c27a63bf
go get: upgraded google.golang.org/grpc v1.37.0 => v1.38.0
➜  gitlab-shell git:(main) ✗ go mod tidy                                   
➜  gitlab-shell git:(main) ✗ go list -m all | wc -l                        
     472
➜  gitlab-shell git:(ash2k/use-moved-gitlab-client) ✗ go list -m all | wc -l
     459