feat: systems and formats

[tupakkatapa]

Added '--format' and '--system' flags to the buidl script.

This means that you can now build any combination of the supported formats and systems on command:

echo $json_data | nix run .#buidl -- -b homestakeros -n foobar -f isoImage -s aarch64-linux

This functionality works by generating nixosConfigurations attributes in the flake for every possible combination of these parameters for each configured host.

Attribute names are formatted as follows: 'name-system-format', for example:

[I] kari@torque ~/W/HomestakerOS (feat/format)> nix eval --json .#nixosConfigurations --apply builtins.attrNames --no-warn-dirty | jq -r '.[]'
foobar-aarch64-linux-isoImage
foobar-aarch64-linux-kexecTree
foobar-x86_64-linux-isoImage
foobar-x86_64-linux-kexecTree

Despite having multiple nixosConfigurations entries, the hosts will still only have one directory at webui/public/nixosConfigurations and nixosConfigurations.

[tupakkatapa]

This PR requires changes to the frontend, hence the draft.

EDIT: Here is some more information for the record. The frontend should include "rogue" options for the --format and --system parameters, as they are unrelated to the module options, aka the schema. Therefore, the logic for handling these options should be implemented entirely on the frontend side, which will then pass the appropriate flags to nix run .#buidl based on these options.