Use GithubURL methods for github url construction

[viktorasl]

In #2622 GithubURL was introduced which should be used for all Github URL building across the app.

1. use concrete methods (i.e GithubURL.codeBlob) for all URL buildings
2. cover w/ unit tests

[viktorasl]

#1121 is a bit related I think because having a nested struct for each Repo node like Issue, PR, ... would make Github URL construction easier

struct RepoPath {
  let owner: String
  let repo: String
}

[RuiAAPeres]

This seems like an interesting issue. Is anyone working on it? If not I could give it a spin. 😅

[rizwankce]

@RuiAAPeres it's all yours