Proposal: make squash-merging the default behavior for gitlab MRs

[Nate Graham]

Hello folks,
I've been told that our Sysadmins have developed some tooling capable of 
checking the "Squash when merging" checkbox by default for new Merge 
Requests. This would be a downstream solution to 
https://gitlab.com/gitlab-org/gitlab/-/issues/222175.

I'd like to propose that this be done as a sane default for new Merge 
Requests. Now, personally I have gotten used to the alternative "curate 
your MR's git history" approach and have written documentation for it at 
https://community.kde.org/Infrastructure/GitLab#Curating_your_merge_request_commit_history.

However, it remains a fairly advanced workflow which is challenging for 
newcomers, drive-by-developers, and people not as familiar with git. For 
these people, squash-merging makes much more sense, and when they forget 
to check that checkbox and someone merges their work, the result is tons 
of garbage commits in the git history.

Accordingly, I think squash-merging makes sense as the default value to 
avoid this. People who are comfortable with the "curated MR commit 
history" workflow will of course still be able to turn it off. IMO it 
makes more sense to ask experts to turn it off than to ask newcomers and 
novices to turn it on.

Thoughts?

Nate