reboot(role): intro. reboot role, which handles local conns. gracefully

Also use this role instead of plain ansible.builtin.reboot.
This is in preparation for using ansible_pull as we don't want to have
ansible.builtin.reboot fail local playbook runs.

roles/reboot/README.md

@@ -0,0 +1,26 @@
+# Role `reboot`
+
+A role for rebooting a host, which also handles local connections gracefully.
+
+## Optional Arguments
+
+- `reboot__local_handling`: How to handle reboot on local connections. The default mode is `none`.  
+  Possible choices:
+  - `none`: Just runs `ansible.builtin.reboot`, which would fail on local connections.
+  - `ignore`: Just doesn't reboot on local connections.
+  - `file`: Doesn't reboot on local connections and instead touches the file defined by `reboot__local_handling_file`.
+- `reboot__local_handling_file`: The file to touch, if `reboot__local_handling` is `file`. Defaults to `/var/run/ansible-reboot-required`.
+
+## Usage in a Handler
+
+Since a reboot should often be triggered from a handler and since handlers can't include or import roles, this roles logic can also be run by including the `main.yaml` task using `ansible.builtin.include_tasks` as a workaround.  
+When doing so, arguments should be specified explicitly as necessary (so at least `reboot__local_handling`) as the default role inclusion mechanisms like setting default values don't work.
+
+An example handler would look like this:
+
+```yaml
+- name: reboot the system
+  ansible.builtin.include_tasks: "../../reboot/tasks/main.yaml"
+  vars:
+    reboot__local_handling: ignore
+```