Make --network accept a file argument and add a --flake flag

[talyz]

To make it possible to keep multiple network definitions in the same directory, make the --network flag accept a file in addition to a directory. Also, add a corresponding --flake flag and create short flags for both (-n and -f respectively).

[roberth]

This needs documentation and tests.

We have unit tests in tests.py and the tests directory, or NixOS/nixpkgs#142035 could be added here for end to end tests.

Not sure if eval-machine-info needs to use the name, instead of nixopsConfigurations.default. Perhaps that should be independent and part of the flake fragment: --flake .#other-deployment.

Documentation can be updated in doc/manual/nixops.rst

[talyz]

This needs documentation and tests.

We have unit tests in tests.py and the tests directory, or NixOS/nixpkgs#142035 could be added here for end to end tests.

I'm not sure how to add this to the unit tests - it doesn't really feel suited for it. The NixOS test could be updated for it, though.

Not sure if eval-machine-info needs to use the name, instead of nixopsConfigurations.default. Perhaps that should be independent and part of the flake fragment: --flake .#other-deployment.

I'm not really sure what this is referring to in relation to this change.

Documentation can be updated in doc/manual/nixops.rst

I've added some basic parameter documentation now and removed the references I could find to the previous -n flag. There's more to document and more in the documentation to update, but I think it makes more sense to do a bigger rewrite when we know how the interface looks - should deployments and the legacy backend be removed or should legacy deployments be fixed instead? As I see it, the prior alternative would require more substantial documentation updates (and be a lot of work in general), while the latter would give us a confusing UX with a lot of old cruft.

[pasqui23]

Suggested change

	if args.network_path is not None:
	if args.network_path is not None and args.flake_path is not None:
	raise ValueError("You can only provide one of either -f or -n")
	if args.network_path is not None:

[talyz]

This is already covered by argparse, since --network and --flake are put into a mutually exclusive group.