[RDBMS] az postgres flexible-server create: Change database name field to default to None

Author: Matthew Boentoro

src/azure-cli/azure/cli/command_modules/rdbms/_params.py

@@ -628,7 +628,7 @@ def _flexible_server_params(command_group):
                 c.argument('cluster_size', default=None, arg_type=create_node_count_arg_type)
                 c.argument('zonal_resiliency', arg_type=zonal_resiliency_arg_type, default="Disabled")
                 c.argument('allow_same_zone', arg_type=allow_same_zone_arg_type, default=False)
-                c.argument('database_name', arg_type=database_name_create_arg_type)
+                c.argument('database_name', default=None, arg_type=database_name_arg_type)
             elif command_group == 'mysql':
                 c.argument('tier', default='Burstable', arg_type=tier_arg_type)
                 c.argument('sku_name', default='Standard_B1ms', arg_type=sku_name_arg_type)