Add ListAppRepositories method to VCS

[EyalDelarea]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• I used go fmt ./... for formatting the code before submitting the pull request.
• This feature is included on all supported VCS providers - GitHub, Bitbucket cloud, Bitbucket server, GitLab and Azure Repos.
• I added the relevant documentation for the new feature.

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✨ Add ListAppRepositories Function to VCS Client Interface

This PR introduces a new function ListAppRepositories to the VcsClient interface, currently implemented only for GitHub.

✅ What It Does
• Adds support for fetching GitHub App-accessible repositories using the installation/repositories endpoint.

⚙️ Why Only GitHub?

Currently, GitHub is the only provider where:
• App-based repo access is a common pattern (via installations).
• There’s a clear, supported API endpoint for listing them.

The interface was designed to support future implementations for GitLab, Bitbucket, etc., once similar functionality is available or required.

📘 Usage Example

ctx := context.Background()
appRepositories, err := client.ListAppRepositories(ctx)
for _, repo := range appRepositories {
    fmt.Println(repo.FullName, repo.CloneURL)
}

[eranturgeman]

What identifies a repository as an "App repository"? what is passed in the context that prevents getting all existing repositories?

[EyalDelarea]

Basically it has more fields and context then our basic repository object.
this is again to not interfere with the current objects and logic and trying to separate them as much as possible for now.

I agree that they could be merged, but as this is changing by the demands, i wanted to keep them separated for now at least.

[eranturgeman]

please ensure we cannot get nil pointer dereference (since you declare the results but doesn't init is using 'make')

[eranturgeman]

Looks good! please see my notes

[EyalDelarea]

@eranturgeman if you can merge this once you are ready.

[github-actions]

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