Update rover login to respect `-c` switch and be able to log into available sovereign clouds.

As best as I can tell, while the `-c` switch is there to set sovereign clouds, it does not appear the `rover login` command uses it at all.

As a workaround, I was able to log directly in to Azure Government using the az cli and then I could use `rover`.

I believe that somewhere near [here](https://github.com/aztfmod/rover/blob/befef5855c03b680747d5d76ec6279e985c878ea/scripts/functions.sh#L263) that another if statement needs to be added, and if `-c` is set, to execute an `az cloud set --name ` prior to executing `az login`

Start in scripts/functions.sh near line 263 and trace how the rover login command handles the -c switch before calling az login. Verify the expected behavior with a sovereign Azure cloud, including that the selected cloud is applied before login and that the existing default-cloud flow still works.

Written by the indexing model from the issue text.