Clarify status for Draft and Under Review ADRs/OEPs

The following PR is a minor update to OEP-1 and OEP-19, clarifying how to denote the intention to merge a Provisional ADR or OEP. See docs: clarify status for Draft and Under Review ADRs/OEPs.

Since this is a minor clarification, it will not go through an extended formal review period. However, you still may be interested in how to do this.

The update has been merged with some slight adjustments to make it more flexible, just in case you read the earlier version.