Optionally enforce semver label

[JAForbes]

A feature idea for pr-release that came out of this discussion

I imagine this would be a simple branch check that runs alongside the test suite for a given PR. It pulls the label information down for the given PR and if there isn't an explicit semver label it exits with a non zero code.

This would run on the feature branch push, so a new github action/template would be needed.

CC @StephanHoyer @dead-claudia