feat: add github repo struct to project service model

[jan-zabloudil]

I have realized it will be much more convenient to have a GithubRepo struct (which will contain parsed slugs) in the service model (and consequently in the repository model).

Why? Because when handling webhook requests, slugs will be provided as the repository identifier. This will simplify the process, i could directly do:

WHERE owner_slug = @ownerSlug AND repo_slug = @repoSlug

In this PR, I only demonstrate how it would be implemented. If you like this approach, I will also update the repository model and modify the GitHub client methods to accept svcmodel.GithubRepo instead of URLs, etc.

I believe this is also a good step towards the larger GitHub refactoring. After the refactoring, you will have a separate entity for the GitHub repository identifier (such as slugs etc.)

[bolshakoff]

But in #109 I can see that chances are, in case of Release, GitHub Release fields might end up simply a part of Release model, and splitted out later on, together with db layer.

In this case, consider employing the same principle also here, i.e. GithubOwnerSlug, GithubRepoSlug and (potentially) dynamically generated GithubRepoURL simply as a part of Project model. 👌

[jan-zabloudil]

I will stick with separate struct here:

I can simply pass the struct from github client:

func (c *Client) GetGithubRepoFromRawURL(rawURL string) (svcmodel.GithubRepo, error) {

I can easily check if github repo is set:

projects.GithubRepo != nil

.....