Extend the cephadm commands to allow defaults and extras

etc/kayobe/cephadm.yml

@@ -86,8 +86,14 @@ cephadm_cluster_network: "{{ storage_mgmt_net_name | net_cidr }}"
 # stackhpc.cephadm.commands for format. Pre commands run before the rest of the
 # post-deployment configuration, post commands run after the rest of the
 # post-deployment configuration.
-#cephadm_commands_pre:
-#cephadm_commands_post:
+cephadm_commands_pre: "{{ cephadm_commands_pre_default + cephadm_commands_pre_extra }}"
+cephadm_commands_post: "{{ cephadm_commands_post_default + cephadm_commands_post_extra }}"
+
+cephadm_commands_pre_default: []
+cephadm_commands_pre_extra: []
+
+cephadm_commands_post_default: "{{ ['mgr module enable prometheus'] if kolla_enable_prometheus_ceph_mgr_exporter | bool else [] }}"
+cephadm_commands_post_extra: []
 
 ###############################################################################
 # Kolla Ceph auto-configuration.

releasenotes/notes/cephadm-pre-post-commands-now-have-defaults-b42ce9b13fa6d63b.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    The Cephadm pre and post commands now support default commands with the
+    variables ``cephadm_commands_pre_default`` and
+    ``cephadm_commands_post_default``. As such, any extra commands should be
+    added to the variables ``cephadm_commands_pre_extra`` and
+    ``cephadm_commands_post_extra``.