ref(inventory): Split up inventory into group vars

One inventory targets a local machine (`inv-local.yaml`, chosen by default)
while the other targets a chrooted installation accessible from another
system, usually in the `/mnt/void` directory (`inv-chroot.yaml`, has to
be called like `ansible-playbook -i inv-chroot.yaml`).

roles/user/defaults/main.yaml

@@ -0,0 +1,18 @@
+user_pass_salt: supersecretsalt
+user_name: voidboi
+user_pass: voidlinux
+user_shell: zsh
+user_shell: zsh
+user_groups:
+  - wheel
+  - _seatd # TODO: This will error if it does not exist? (seatd not installed)
+  - dialout
+  - disk
+  - input
+  - kvm
+  - lp
+  - plugdev
+  - scanner
+  - storage
+  - usbmon
+