Handle new `PrivilegeLevelChangeAction`

[michalpristas]

PrivilegeLevelChangeAction:
 type: object
 properties:
   id:
     type: string
     description: Unique identifier for the action.
   type:
     type: string
     description: Type of the action.
   unprivileged:
     type: bool
   user_info:
     $ref: '#/definitions/UserInfo'
     description: Information about the user (ignored when unprivileged is false).
 required:
   - id
   - type
   - unprivileged
UserInfo:
 type: object
 properties:
   username:
     type: string
     description: Username of the user (if not provided, defaults to ElasticUsername).
   groupname:
     type: string
     description: Groupname of the user (if not provided, defaults to ElasticGroupName).
   password:
     type: string
     description: Password of the user (if not provided, no password is set.
 required: []