feat(gitlab): add merge method check

[viceice]

If merge_methodis not merge we need to force rebase our branches.

Closes #5565

[viceice]

No live test yet. Maybe safe anyway?

[rarkins]

I just realized something - we need to check when this field was introduced. Otherwise if there's older GitLab versions which don't support the field then they'll start always rebasing.

[viceice]

ok, i'll look at the api

[viceice]

https://docs.gitlab.com/ee/policy/maintenance.html

looks like they only support the latest 3 versions.

I can't find when try introduced the property, but i think it was long time ago. (at least readonly)

but to be safe, we can check existance.

[github-actions]

🎉 This PR is included in version 19.148.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

Your semantic-release bot 📦🚀

[viceice]

looks like https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/14272 introduced it in version 10.1.

Older versions have had other properties. Should we support older versions than 10.1, which are no longer supported?

[rarkins]

We should support whatever GitLab says is supported, but ideally not break older stuff also if we can avoid it.

[viceice]

We do not break it, we only force a rebase if we fall behind on version less than 10.1 🙈

[viceice]

a simple fix for older versions would be config.mergeMethod = res.body.merge_method || 'merge';