Add status check for PRs that can only be merged after a specific date

[IstoraMandiri]

cc @DonaldMcIntyre , this would prevent articles from getting merged too early.

Will need to do a bit of research in the best way to achieve this but should be possible with https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/defining-the-mergeability-of-pull-requests

[gitr0n1n]

Merge scheduling? Would be good for tweets too.