AgentImageCleanup: Agent handles new type of NMP

[LiilyZhang]

The following section will be added to NMP for handling image on the agent:

“image_policy”: {
    “removal”: [
          {
              “image_name”: “image1:0.0.1”,
              “delete_after_minutes”: 30,
              “agent_downloaded_only”: true
          },
         {
             “image_name”: “*”,
             “delete_after_minutes”: 60,
             “agent_downloaded_only”: false
         }
    ]
}