Simplify rebase instructions in PRs

[rarkins]

Tell us more.

We support three ways to rebase:

• rebase/retry checkbox: preferred by github, gitlab, gitea
• rebase label: preferred by azure, gerrit soon
• renaming PR title: bitbucket, bitbucket server, codecommit [none support labels]

We today mention rebasing three possible times:

• In the PR body itself
• In a PR comment if the PR is edited
• In a PR comment if there's an artifacts error

I think that we can remove "exact" instructions from the two PR comments and instead just say "you manually request a rebase/retry".

Then we are left with customizing the PR body only. I think we should mention only the preferred way per platform there.

Final question is: do we need to specify the exact rebaseLabel, or would that be intuitive enough to most users if we just say "add the rebase label to this PR"?

Once we decide on this, we can simplify the massageMarkdown() functions

[viceice]

i think the generic rebase label is enough.

[felipecrs]

I disagree. How would users know what is the correct label? Looking up in the documentation? Sounds unnecessarily difficult, considering we can address this right in the PR description.

(And considering this can be overridden by self-hosting and even by repository)

[felipecrs]

I would say this can be closed considering:

• feat(gerrit): add support for labels through hashtags #35900
• feat(gerrit): suggest use of rebase hashtag #36955