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/actions-show-response.json

@@ -22,5 +22,6 @@
         "message": "Welcome"
     },
     "action_type": "nop",
-    "created_at": "2018-04-10T11:59:12.725147+00:00"
-}
+    "created_at": "2018-04-10T11:59:12.725147+00:00",
+    "status_message": null
+}