Preserve branch protection status when importing from GitHub

Problem to solve

As described by @KOLANICH:

When a one imports a repo from GitHub, its master branch automatically gets protection, even if on GitHub it was not protected.

It causes some problems. For example if I like to rewrite history now I have to walk all therepos and unprotect their master branches.

Proposal

Branch protection status should be cloned from GitHub.

We decided to always use the strictest set of rules and ensure that the logic isn't about "default" vs. "non-default" (see discussion).

Calculated GitLab branch protection rule	State of existing branch in GitHub	Result
Unprotected	Unprotected	Unprotected
Protected	Unprotected	Protected
Unprotected	Protected	Protected
Protected	Protected	Protected with the strictest protection rules

References

• https://docs.github.com/en/rest/branches/branch-protection