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>

releasenotes/notes/blueprint-add-skip-actions-4a5a997dc1133f13.yaml

@@ -0,0 +1,20 @@
+---
+features:
+  - |
+    A new state ``SKIPPED`` has been added to the Actions. Actions can reach this state
+    in two situations:
+
+    * Watcher detects a specific pre-defined condition in the `pre_condition` phase.
+
+    * An admin sets the state to SKIPPED using a call to the new Patch API `/actions/{action_id}`
+      before the action plan is started.
+
+    An action in ``SKIPPED`` state will not be executed by Watcher as part of an ActionPlan
+    run.
+
+    Additionally, a new field ``status_message`` has been added to Audits, ActionPlans and
+    Actions which will be used to provide additional details about the state of an object.
+
+    All these changes have been introduced in a new Watcher ``API microversion 1.5``.
+
+    For additional information, see the API reference.