Add Geo-Replicated SQL MI autorotation note

[lukecalderon]

In sql-docs\azure-sql\database\transparent-data-encryption-byok-key-rotation.md

Added a note to provide clarification when using the same default TDE encryptor across a failover group. This is mentioned in a different page here; however, the article I've updated contradicts the configuration.

The behaviour has been confirmed by the SQL MI Product Group via a support ticket.