Releasing can be blocked

What does this MR do?

Allows schema authors to block releasing if for any reason a merged MR should not be immediately released.

What are the relevant issue numbers?

n/a

Checklist

• Ensure changes can be built upon without requiring a breaking change, see Building for Extensibility.
• Review and add/update tests for this feature/bug.
• Add an entry to the CHANGELOG if required, with the appropriate version. See Classifying Changes.
• Assign the MR to the appropriate person/people for review.