Clean up module documentation (#36909)

* Clean up module documentation

This PR includes:
- Removal of `default: None` (and variations)
- Removal of `required: false`
- Fixing booleans and `type: bool` where required

* Fix remaining (new) validation issues

lib/ansible/modules/cloud/openstack/os_keystone_domain.py

@@ -32,13 +32,11 @@ options:
    description:
      description:
         - Description of the domain
-     required: false
-     default: None
    enabled:
      description:
         - Is the domain enabled
-     required: false
-     default: True
+     type: bool
+     default: 'yes'
    state:
      description:
        - Should the resource be present or absent.
@@ -47,7 +45,6 @@ options:
    availability_zone:
      description:
        - Ignored. Present for backwards compatibility
-     required: false
 requirements:
     - "python >= 2.6"
     - "shade"