Add GitHub workflow, that helps SIG maintainers to keep track of spec changes

What are you trying to achieve?

See https://github.com/open-telemetry/community/issues/2087

As suggested there, I propose that we add a workflow to the spec repo that is triggered on release and raises an issue on the language SIGs with the release notes. The SIG maintainers can then handle the issue within their own triage process.

I would suggest to roll this out for 1-2 SIGs first and then add the other ones later.

I am happy to help with building that workflow, I created this issue beforehand to verify that this is what we want to do.