Report AlloyDB usage in usage ping

Currently we report various flavors of PostgreSQL, we should also try to detect if any customers use AlloyDB in a similar fashion.

Similar to other checks, we can try to detect some of the AlloyDB specific database flags - https://cloud.google.com/alloydb/docs/reference/database-flags, for example alloydb.* or google_columnar_engine.enabled.

Definition of Done

• AlloyDB is a detectable flavor in usage ping