[Feature]: Add information primary database to Get-AzSqlDatabase command for read-only replica databases

### Description of the new feature

The current implementation of Get-AzSqlDatabase does only include a property _SecondaryType_ which tells if the database is a secondary (e.g. Named replica). It would be great if there were additional properties with information about the primary database to which the secondary is linked to. This information is available when executing the Azure CLI statement _az sql db replica list-links_.

I also tried to get the information through a Get-AzResource statement. This did not give me the information either.

### Proposed implementation details (optional)

It would be great if some or all of the following properties would be available.

```json
{
"PrimaryResourceId": "",
"PrimaryResourceGroupName": "",
"PrimaryServerName": "",
"PrimaryDatabaseName": ""
}
```