docs: Update apt_key.py add requirements of gpg (#61552)

* docs: Update apt_key.py add requirements of gpg. The module needs to have gpg installed, otherwise it will end up with error {"changed": false, "msg": "Failed to find required executable gpg in paths: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

Co-Authored-By: John R Barker <john@johnrbarker.com>

lib/ansible/modules/packaging/os/apt_key.py

@@ -29,6 +29,8 @@ notes:
       To generate a full-fingerprint imported key: C(apt-key adv --list-public-keys --with-fingerprint --with-colons)."
     - If you specify both the key id and the URL with C(state=present), the task can verify or add the key as needed.
     - Adding a new key requires an apt cache update (e.g. using the apt module's update_cache option)
+requirements:
+    - gpg
 options:
     id:
         description: