[Monitor] cannot get metric's time_grain through get method

It seems that the ```time_grain``` field won't return in the get process. Is it a correct behavior?
https://docs.microsoft.com/en-us/rest/api/monitor/diagnosticsettings/get

Start with the linked Azure Monitor diagnosticsettings/get documentation and inspect how the time_grain field is represented in the corresponding REST API specification. Compare the documented GET response with the reported behavior and determine whether the specification needs correction or the behavior is intentional. Done means the expected handling of time_grain is clearly established and reflected in the issue or specification.

Written by the indexing model from the issue text.