ref: Use default branch as merge target instead of parent detection

[kamilogorek]

This is WiP to fix #327

We remove automatic branch detection, use the default as the main source of truth, but allow for overriding it through the GH Action input (this needs to be added per repository, inside .github/workflows/release.yml in with clause).

Related required issues:
getsentry/action-prepare-release#23
getsentry/publish#838

[kamilogorek]

cc @BYK

[BYK]

This will require reopening #239. I think we can still consider using git merge-target and then find the branch name from there?

[jan-auer]

Thanks, LGTM.

Could you please add this to the readme as well? The merge target is not listed at all in the publish section yet.

[jan-auer]

@BYK can you elaborate why this would reopen #239? Together with the linked PRs, this gives enough control to choose the merge target manually in the few cases this is necessary.

[lobsterkatie]

this needs to be added per repository, inside .github/workflows/release.yml in with clause

Specifically what needs to be added? Could you link to an example here for individual repo maintainers to follow?

[kamilogorek]

@lobsterkatie I updated the readme yesterday here - https://github.com/getsentry/publish#merge-target

[BYK]

@jan-auer

@BYK can you elaborate why this would reopen #239? Together with the linked PRs, this gives enough control to choose the merge target manually in the few cases this is necessary.

Oh, right my bad. I thought this PR was doing away with the merge-target option completely. It is now more error-prone and cumbersome to achieve #239 as one has to remember to both have this config in their release workflow and not forget to add the correct merge target manually without any validation ahead of time.

I agree that it is still better than merging to the wrong target for the most common case but the experience and safety is far from being ideal.