feat(server): allow setting user_data for rebuild (#794)

##### SUMMARY
`user_data` is now a supported field for rebuilds.
See
https://docs.hetzner.cloud/changelog#2026-01-16-server-rebuild-with-user-data

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: jo <ljonas@riseup.net>

changelogs/fragments/server-rebuild-user-data.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - server - Rebuilding a Server now supports the ``user_data`` argument.

plugins/modules/server.py

@@ -126,7 +126,7 @@ options:
         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.
+            - Used during the server creation or server rebuild.
         type: str
     rescue_mode:
         description:
@@ -930,8 +930,13 @@ class AnsibleHCloudServer(AnsibleHCloud):
             self.module.fail_on_missing_params(required_params=["image"])
             try:
                 if not self.module.check_mode:
-                    image = self._get_image(self.hcloud_server.server_type)
-                    resp = self.client.servers.rebuild(self.hcloud_server, image)
+                    params = {
+                        "image": self._get_image(self.hcloud_server.server_type),
+                    }
+                    if (value := self.module.params.get("user_data")) is not None:
+                        params["user_data"] = value
+
+                    resp = self.client.servers.rebuild(self.hcloud_server, **params)
                     # When we rebuild the server progress takes some more time.
                     resp.action.wait_until_finished(max_retries=202)  # 202 retries >= 1002 seconds
                 self._mark_as_changed()

tests/integration/targets/server/tasks/test_basic.yml

@@ -257,6 +257,10 @@
   hetzner.hcloud.server:
     name: "{{ hcloud_server_name }}"
     image: "{{ hcloud_image_name }}"
+    user_data: |
+      #cloud-config
+      packages:
+        - curl
     state: rebuild
   register: result_after_test
 - name: verify rebuild server