Update scope-of-support-gitlab-self-managed.html.md to call out alpha/beta...
Update scope-of-support-gitlab-self-managed.html.md to call out alpha/beta feature support offerings.
This came about from a slack thread, and a conversation with Cindy P.
Effectively, we want to support features in beta, but keep the priority low (making sure beta issues don't take precedence over "released features").
We also want to make sure to make it clear that Alpha features will not be covered via a support contract.