cephadm-adopt: inform users about cephadm

Print a message at the end of the playbook to inform users that they
don't have to user ceph-ansible playbooks anymore as everything else
need to be done via cephadm (day 2 operation).
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>

infrastructure-playbooks/cephadm-adopt.yml

@@ -1049,3 +1049,10 @@
       changed_when: false
       environment:
         CEPHADM_IMAGE: '{{ ceph_docker_registry }}/{{ ceph_docker_image }}:{{ ceph_docker_image_tag }}'
+
+    - name: inform users about cephadm
+      debug:
+        msg: |
+          This Ceph cluster is now managed by cephadm. Any new changes to the
+          cluster need to be achieved by using the cephadm CLI and you don't
+          need to use ceph-ansible playbooks anymore.