WIP: a very basic metric endpoint

Use the following payloads to test the functionality of the endpoint.

handshake: 
{ "method": "handshake.hello", "v": 1, "target": "endpoint", "source": "agentA",  "params": {        "agent_id": "agentID"    },    "manifest": null }

metrics:
{ "method": "check_metrics.post", "v": 1, "target": "endpoint", "source": "agentA",  "params": {  "msg": "hello world"  }  }