Feature request: Enforce PR merge order

Sometimes it is important that one pull request is merged before another one. Currently there is no way to enforce this. I could see this working in a few different ways:

• Writing blocked by pr CODE" in pull request description. (This is what I do now but it it is risky since there is no enforcement yet.)
• A "blocked by" field on the PR page that allows you to put in another PR that has to be merged/completed first.

ps: Thanks for all the support and frequent updates!