docs: add note that server.user_data is used by cloud-init (#786)

##### SUMMARY
I was looking for "cloud" or "cloud-init" within the documentation
without any luck. Maybe this will help someone else finding the
appropriate option.

##### ISSUE TYPE
- Docs Pull Request

##### COMPONENT NAME
`hetzner.hcloud.server`

---------

Co-authored-by: Jonas L. <jooola@users.noreply.github.com>

plugins/modules/server.py

@@ -125,6 +125,7 @@ options:
     user_data:
         description:
             - User Data to be passed to the server on creation.
+            - C(cloud-init), C(ignition) or similar provisioning tools may retrieve user configuration from the Server's C(user_data).
             - Only used during the server creation.
         type: str
     rescue_mode:
@@ -178,6 +179,16 @@ EXAMPLES = """
       - me@myorganisation
     state: present
 
+- name: Create a basic server with additional cloud-init data disabling SSH password authentication
+  hetzner.hcloud.server:
+    name: my-server
+    server_type: cpx22
+    image: ubuntu-22.04
+    user_data: |
+      #cloud-config
+      ssh_pwauth: false
+    state: present
+
 - name: Resize an existing server
   hetzner.hcloud.server:
     name: my-server