feat(src/nixos-anywhere): use tar and ssh instead of rsync

[Prince213]

Resolves #260. Closes #295.

This PR replaces use of rsync with a combination of tar and ssh. It's an alternative solution to #295, but it avoid the problem as per #295 (comment). Also, directly copying with scp will not preserve symbolic links, which isn't a issue with this PR.

One notable change is that extra_files is assumed to be a directory, though there doesn't seem to be much case for it to be (multiple) files (checked within the repo), which isn't useful anyway because the exact path can't be easily specified (see also #283).

[Prince213]

@Mic92 please take a look.

[Mic92]

@mergify queue

[mergify]

queue

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[Mic92]

@Mergifyio rebase

[mergify]

rebase

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[Prince213]

Sorry for that @Mic92, authorized now. Please try again, it should now work.

Edit: Never mind, just saw #325.