API changes for skipped actions: patch actions and status_message

This patch implements the changes in the API required for the
skipped action blueprint. It includes:

- New field `status_message` is visible in API get calls for Audits,
  ActionPlans and Audits.
- New Patch call is added to `/actions/{action_id}` which allows to
  manually move actions in PENDING state to SKIPPED for ActionPlans
  which have not been started.
- A new API microversion 1.5 is added for these changes.

It also adds requried tests and documentation.

Implements: blueprint add-skip-actions

Assisted-By: Cursor (claude-4-sonnet)

Change-Id: I71fb9af76085e5941a7fd3e9e4c89d6f3a3ada47
Signed-off-by: Alfredo Moralejo <amoralej@redhat.com>

api-ref/source/samples/audit-show-response.json

@@ -51,5 +51,6 @@
     "updated_at": "2018-04-06T11:54:01.266447+00:00",
     "hostname": "controller",
     "start_time": null,
-    "end_time": null
+    "end_time": null,
+    "status_message": null
 }