[RULE] Add support for Defender for Cloud for Azure Database for MySQL for the flexible deployment model

### Existing rule

Azure.MySQL.DefenderCloud

### Suggested rule

The flexible deployment model now supports Defender for Cloud for Azure Database for MySQL.

It is done by configuring `Microsoft.DBforMySQL/flexibleServers/advancedThreatProtectionSettings`.

This resource resource is read-only.

It can be enabled through either of the following methods:

- Subscription Level Enablement: Enable the `open-source relational databases` resource type under the Microsoft Defender for Cloud Databases plan for the subscription where the server is located.
- Resource Level Enablement: Manually enable Microsoft Defender for Cloud for the specific resource via the Azure portal under the resource blade.

### Pillar

Security

### Additional context

https://azure.microsoft.com/updates/generally-available-defender-for-cloud-supports-azure-database-for-mysql-flexible-server