Add option to `az storage share generate-sas` to generate full URL rather than just SAS value.

**Is your feature request related to a problem? Please describe.**
When using the `az storage share generate-sas` command to generate a Shared Access Signature for an Azure Storage File Share, the result of the command is just the raw SAS value, such as:

```
"se=2019-10-31T23%3A17%3A07Z&sp=rw&sv=2018-11-09&sr=s&sig=EhY7UeRqG39jQ2Nhcv0XthtUl/8C/vsN5mApuFYXsB4%3D"
```

If you want to generate a full URL including the SAS key, to use in a tool such as Azure Storage Explorer, you have to jump through a few hoops with formatting and other commands, which is inconvenient.

**Describe the solution you'd like**
It would be very useful to be able to produce a full URL with SAS from this command directly.

**Describe alternatives you've considered**
A new parameter that alters how the result is provided would be useful, for example `--as-url` or something similar.