[Feature Request]: PostgreSQL flexibleServers missing AAD configuration and administrators #3563

Description

I want to enable AAD authentication only and add AAD admins to the PostgreSQL flexibleServers.

The PostgreSQL flexibleServers module is missing authConfig section, can't enable AAD authentication and add the AAD administrators.

Missing sections :
authConfig: {
activeDirectoryAuth: 'string'
passwordAuth: 'string'
tenantId: 'string'
}

Please make administratorLogin and administratorLoginPassword parameters optional as I want to set AAD authentication only. And a new parameter to pass AAD administrators.