Add option to set UUID of partitions

[Rua]

At the moment, it seems that the UUID of a partition is randomly generated by sgdisk at the time it is created. This can potentially lead to reproduceability problems if things elsewhere on the system refer to that UUID. UUID is also intended to uniquely identify a partition, rather than the label/device name as disko currently does by default. It would be useful to be able to specify the partition UUID in the configuration, so that it can be reproduced, and referred to deterministically that way.

[Mic92]

Sounds like an acceptable feature to make this configurable. You would need to add this to lib/types/gpt.nix