Go's semantic import versioning requires v2+ modules to include the
major version in the module path. This enables using proper version
tags (v3.x.x) instead of pseudo-versions.
Updated module path: code.gitcaddy.com/server/v3
1 Move `IsRepositoryModelOrDirExist` and `CheckCreateRepository` to
service layer
2 Use `gitrepo.Pushxxx` instead of `git.Push` when possible
3 use `gitrepo.Clonexxx` instead of `gitrepo.Clone` when possible
