feat: Add new keepUpdatedLabel config setting

[mheffner]

Changes

This adds the keepUpdatedLabel config setting.

Adding the keepUpdatedLabel label to a PR makes Renovate behave
as if rebaseWhen were set to behind-base-branch, but only for the given PR. The label is not removed from the PR
after the rebase is complete, unlike rebaseLabel.

This can be useful when you have approved certain PRs and want to keep them updated until they are ready
to be merged. The setting keepUpdatedLabel is best used in conjunction with rebaseWhen set to the
values of never or conflicted that limit rebasing.

Context

The motivation for this change came out of the discussion about managing the use of renovate bot alongside kodiakhq bot: #27328. It was suggested by the Renovate maintainer that a new option could be added that allowed a user to opt-in given PRs to rebase updates.

This provides an implementation of that option from my best understanding of the existing code. It mostly follows the use of rebaseWhen, modifying the behavior if keepUpdatedLabel is set and the label is included on the PR.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

I had expected it should behave like rebaseWhen=behind-base-branch, not auto. Why don't think auto is a better approach? In some cases auto won't update the PR, which would seem like a bug to the user if you've configured a keepUpdatedLabel

[mheffner]

You're right, I would expect this to behave like behind-base-branch. I actually believe that is the behavior of the change set, but that the option setting documentation was wrong. I just pushed a change to update the documentation for the option to what I believe is the behavior here.

I tested this on a repo with the "require branches be up-to-date" setting both on and off. In both cases if the keepUpdatedLabel was applied to a PR, it was rebased. Are there any scenarios you see in the changeset that I may not have handled?

[mheffner]

👀 it looks like reuse.ts doesn't have 100% coverage, I'll take a look at adding something to cover what's missing

[mheffner]

I pushed a commit that should bump reuse.ts coverage to 100%

[mheffner]

@rarkins Ok, I think I've got the final coverage reports back up to 100%. I missed that requirement when I was running tests locally. 🤦 Do you prefer to resolve the open conversations yourself?

[renovate-release]

🎉 This PR is included in version 37.222.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)
• 37.222.0

Your semantic-release bot 📦🚀