feat: Add allow_force_push in ProtectedBranch

[egore]

See https://docs.gitlab.com/ee/api/protected_branches.html

This also applies to the 6.x branch

[jmini]

Looks good to me.

Please also update the file src/test/resources/org/gitlab4j/api/protected-branch.json so that your change is also covered by unit tests.

Those example files should be as close as possible to the real response sent by GitLab (it can also be the example taken from the documentation page) just we do not support null values in the test, so you need to have one explicit value (with the appropriate type) for each attribute (even if in reality 2 attributes can not be set at the same time).

[jmini]

This also applies to the 6.x branch

Yes according to our branching model (see #926) I am applying each change to both branches.
Targeting main is correct in your case.

[jmini]

I have updated the example file