due to GitLab's default API pagination limit. This prevented users from
accessing branches in repositories with more than 20 branches.
Changes:
- Add pagination loop to fetch all branches across multiple pages
- Set per_page to 100 (GitLab's maximum) for efficiency
- Add safety check using x-total header to prevent unnecessary requests
- Follow the same pagination pattern as validateGitlabProvider function
Fixes issue where branch selection was limited to first 20 branches
in repositories with many branches.
