- per-system default.nix now inherits the source tree via `src` (this
allows modules to be optionally imported from `modules/opt/`)
- adds a default config for microvm hosts
- enables systemd-networkd by default
- allows passing in vms
- binds vm nix-store to host nix-store
- allows merging systemd jounals
- adds microvms to palatine-hill
Signed-off-by: ahuston-0 <aliceghuston@gmail.com>
