feat: substitute disk commands by pure golang

[Itxaka]

Currently we require several binaries both on agent and immucore to exist in the system.

This brings packages that might not be needed after install or that are a commodity (mount can be called directly as a syscall for example)

We should have a look into substituting those by a pure golang implementation like https://github.com/diskfs/go-diskfs

That means:

• less dependencies in the underlying OS
• more interoperability between systems (especially libc vs musl)
• smaller images
• less points of failure (required binaries on the install image, on the initramfs, probable desync)

[Itxaka]

potentially we could also build the isos with it but Im not sure it would support all of our options like hybrid isos and such

EDIT: it actually does: https://github.com/diskfs/go-diskfs/blob/master/examples/bootable_iso.go#L44