Add setting all MRs to Draft when first created

@fabiopitino mentioned an idea I'd also had in passing in #25426 (comment 887848978). Discussing how we might prevent pipelines from triggering when an MR is in Draft state...

However, it doesn't stop a pipeline from being created when you accidentally create a MR not in Draft, which is the scenario @bradttp was explaining. For that specific case maybe we could have a setting that always creates a MR as Draft? Is this a different problem to solve?