az monitor metrics list should have a parameter for the unit

**Related command**
az monitor metrics list

**Is your feature request related to a problem? Please describe.**
I would like to define the results per a pre-specified unit, which today is not possible. Nowadays, for instance, I would like to know the memory usage in bytes, and the command only returns results in a percentage of memory usage. The same for hard disk.

**Describe the solution you'd like**
The solution is to add a parameter called --unit with possible values per metric. For instance, percentage or bytes.

**Describe alternatives you've considered**
An alternative solution is to add a field in the JSON results with the total amount of memory or hard disk in bytes, so I can calculate it.