Add custom error handler for missing default branch

[koesie10]

When the GitHub API returns an error for a missing default branch, we will now show a custom error message. This custom error message includes a link to the page to create the branch. The error is detected using the errors field on the response that is now being returned.

Example response:

{
    "message": "Variant analysis failed because controller repository dsp-testing/koesie10-empty-repo does not have a branch 'main'. Please create a 'main' branch in the repository and re-run the variant analysis.",
    "errors": [
        {
            "repository": "dsp-testing/koesie10-empty-repo",
            "default_branch": "main",
            "resource": "Repository",
            "field": "default_branch",
            "code": "missing"
        }
    ]
}

Example error:

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[charisk]

LGTM!