Invalid unix socket address following gRPC upgrade causes connection failures

In !3403 (merged), we upgraded our gRPC version. The new gRPC version has some differences in how unix socket addresses are handled. Gitaly has previously used unix:// prefixed socket paths. This does not work for relative paths with the new gRPC version and we should either use unix:relative/path, unix:/absolute/path or unix:///absolute/path.

There are some places in the codebase where we handle the paths incorrectly, for example: https://gitlab.com/gitlab-org/gitaly/-/blob/86d069ca736dfde9fa61f8476e974c7b8c15a1e9/internal/gitaly/server/server_factory.go#L58. On a quick grep of unix://, there are plenty of more locations we do this in, although not all of them really attempt to dial the address.