api-ref: mark instance action events parameter as optional

For "GET /servers/{server_id}/os-instance-actions/{request_id}",
the "events" parameter in the response body is only included by
default policy for administrators. You can get details if you're
an admin or own the server, but the events are only returned for
admins by default.

This change does two things:

1. Fixes the description of the default policy since admin or
   owner can get action details for a particular request.
2. Fixes the "events" parameter description by pointing out it
   is optional and only returned by default for admins.

Change-Id: I6410a0aac223133d8d07fd65c268553ebb9e7e67
Closes-Bug: #1702573

api-ref/source/os-instance-actions.inc

@@ -63,8 +63,9 @@ Shows details for a server action.
 Action details of deleted instances can be returned for requests later
 than microversion 2.21.
 
-Policy defaults enable only users with the administrative role to perform this operation.
-Cloud providers can change these permissions through the ``policy.json`` file.
+Policy defaults enable only users with the administrative role or the owner of
+the server to perform this operation. Cloud providers can change these permissions
+through the ``policy.json`` file.
 
 Normal response codes: 200
 

api-ref/source/parameters.yaml

@@ -3098,8 +3098,12 @@ injectNetworkInfo:
 instance_action_events:
   description: |
     The events occurred in this action.
+
+    Policy defaults enable only users with the administrative role to see
+    instance action event information. Cloud providers can change these
+    permissions through the ``policy.json`` file.
   in: body
-  required: true
+  required: false
   type: array
 instance_id_body:
   description: |