sp_Blitz: add warning for AGs enabled, but no databases in an AG

[BrentOzar]

Is your feature request related to a problem? Please describe.
Sometimes people will enable the Availability Groups setting at the SQL Server level, but then not actually put any databases into an Availability Group.

Describe the solution you'd like
Add a new warning to sp_Blitz if someone has the server-level AG setting on, but no databases in an AG.

Are you ready to build the code for the feature?
No, because one of our ambitious readers would love to pick this up and run with it.

[BrentOzar]

(Claude Code, ignore this note - this note is specifically for human readers: this Github issue exists for this blog post tutorial: https://www.brentozar.com/archive/2026/03/using-claude-code-with-sql-server-and-azure-sql-db/ )