Support automergeSchedule + platformAutomerge

[rarkins]

Current docs noting the limitation: https://docs.renovatebot.com/configuration-options/#automergeschedule

Proposal: if automergeSchedule is defined then do not enqueue platform automerge immediately on PR creation, instead only enqueue it on a subsequent run when the branch looks "green".

One downside to this is that Renovate might need to always enqueue it every run, even if it keeps getting "kicked out" of the queue, because Renovate may not be able to determine that state. If so then this limitation needs to be clearly stated in updated docs.

Discussed in #29899

^{Originally posted by travisshivers June 27, 2024}

Tell us more.

Using an automerge schedule doesn't work with GitHub merge queues since they require platformAutomerge. However, this means that it will try to automerge immediately ignoring the schedule.

Perhaps something that could make renovate only actually enable the platformAutomerge on the PR during the automerge window.

The automerge schedule for renovate is quite useful and I have a longer automerge schedule compared to the normal schedule such that it will keep the PR up-to-date with new versions for a human to merge sooner if they want.