[FEAT] Move `db list-regions-*` to `db regions *`

[toptobes]

To help declutter the database subcommands, the follow commands could live under a single db regions subcommand:

list-regions-classic      List all available regions for classic Astra DB
                            databases
list-regions-serverless   List all available regions for serverless Astra DB
                            databases
list-regions-vector       List all available regions for vector Astra DB
                            databases

This would also help distinguish them between the list-regions command which is completely different from these three, as that one operations on a specific database, where as list-regions-* lists all potentially available regions.

Old db list-regions-* commands would still work, but they would be hidden from the helptext, and issue a deprecation warning if used, redirecting users to db regions *.

Might need to do something similar for streaming for consistency–TBD