Allow user to enter volume name if default volume name is not found

[omniopal]

[!NOTE] Fixes issue #1

If a user runs bypass-mdm.sh with a volume not named as Macintosh HD it will fail with No such file or directory errors because it can't find the volume.

These changes allow the user to enter their own custom volume name if Macintosh HD is not found. This prevents users from having to reformat and rename to Macintosh HD for this script to work.

I tested this on my end with my volume named APPLE SSD and it worked.

[assafdori]

Looks good, I'll test and merge soon.

[tcler]

I just solved a similar problem in this patch, it will automatically discovering data Volume and root Volume:

https://github.com/assafdori/bypass-mdm/commit/dbff514f7b9e691ef2b468e53d3dc1f4f7297fd1?w=1

Now it works fine on my friend's M1-pro laptop.

BTW: Thanks @assafdori for your great Job! It saved my friend's second-hand Apple laptop

[Neustradamus]

Dear @assafdori,

Any progress on this PR?