feat(wayland): Add display manager greetd and greeter tuigreet

Sets up a login screen using tuigreet. From there the user is thrown
into a shell. Other units/services (usually, the user service `river`)
take care to start an actual wayland session for the user.

books/void_wayland.yaml

@@ -39,6 +39,43 @@
           - xdg-desktop-portal-wlr
         state: present
 
+- name: Set up display manager
+  hosts: target_system
+  become: true
+  vars:
+    greeter_user: _greeter
+  tags:
+    - wayland
+    - greetd
+    - tuigreet
+  tasks:
+    - name: Ensure user group for greeter exists
+      ansible.builtin.group:
+        name: "{{ greeter_user }}"
+        state: present
+
+    - name: Install greetd and tuigreet
+      community.general.xbps:
+        name:
+          - greetd
+          - tuigreet
+        state: present
+
+    - name: Set up tuigreet config for greetd
+      ansible.builtin.template:
+        src: greetd-config.toml.j2
+        dest: "/etc/greetd/config.toml"
+        owner: root
+        group: root
+        mode: 0644
+        force: true
+
+    - name: Activate greetd service
+      ansible.builtin.file:
+        src: "/etc/sv/greetd"
+        dest: "/etc/runit/runsvdir/default/greetd"
+        state: link
+
 - name: Install audio and video for wayland
   hosts: target_system
   become: true