Option to disable update branch by rebase

[jpraet]

Feature Description

In Gitea 1.16 we can update a PR branch using rebase instead of merge. (#16125)

I would like to be able to disable this option through some configuration option.
I think it's often not a good idea to rebase as it is a destructive operation:

• it causes issues when the person/people working on the PR have local changes that have not been pushed yet
• it marks review comments as outdated (force pushing marks all PR comments as outdated #12956)

So, for the workflow in my team I would like to discourage rebasing by not showing the option in the UI.

Screenshots

[jpraet]

Can it be added to the PullRequestsConfig (AllowRebaseUpdate)?
Should it default to true or to false?

[lunny]

Can it be added to the PullRequestsConfig (AllowRebaseUpdate)? Should it default to true or to false?

I think yes, it could be in that struct. To keep compatible as old version, it should be true.