External Drive Support for UTM virtual machines

So that I have more control over disk usage on my machine,
As a UTM user,
I can run UTM images on external drives.

### Acceptance Test - Create Disk Image on External Drive

* Given I have an external drive connected to my machine,
* When I create a new disk image in the UTM application,
* Then I should be able to select the external drive as the storage location,
* And a performance warning should pop up informing me about potential issues with using an external drive.

### Acceptance Test - Move Disk Image to External Drive

* Given I have an external drive connected to my machine,
* And I have an existing disk image stored on my internal drive,
* When I move the disk image to the external drive using the UTM application,
* Then the operation should complete successfully,
* And a performance warning should pop up informing me about potential issues with using an external drive.

### Acceptance Test - Restrict NAS Drive Usage

* Given I have a NAS drive connected to my network,
* When I try to create or move a disk image to the NAS drive using the UTM application,
* Then the application should not allow the operation,
* And I should receive an error message stating that NAS drives are not supported.