Each project should define a default branch

[KrauseFx]

Right now, we have multiple occurrences (about 8) where we fallback to the default branch "master". While most git setups have master as default branch, we probably want a per-project setting of the default/main branch.

Instead of a setting, it seems enough to fetch it on the fly and cache it somewhere (https://stackoverflow.com/a/44750379/445598)

[fastlane-danger-bot]

We decided to pause our work on fastlane.ci to focus on the core fastlane product as we have a lot on the roadmap. You can find more information on the main GitHub page. This issue will be auto-closed 👍