Add ability for data-plane services to surface diagnostics to the control-plane

[doylemark]

Why

This PR defines new traits that enable collection of diagnostics from various services within the data-plane.
By implementing the Diagnosable trait, a service can report aribtary JSON diagnostics to the control-plane which are then logged.

These diagnostics are surfaced by the data-plane to the control-plane, when the control-plane requests a healthcheck. Although they are surfaced alongside the healthcheck, they are not considered part of the healthcheck itself.
The is_healthy method which is used to describe the health of the enclave to ECS, currently only considers the status of the user process.

In the future more services can surface diagnostics using this implementation, at that point it may be useful to consider certain diagnostics as part of the healthcheck.

How

Diagnostics will be surface to the control-plane as serialized JSON.

{
  "controlPlane": "Ok",
  "dataPlane": {
    "Initialized": {
      "user_process": {
        "Initialized": {
          "Response": {
            "status_code": 200
            "body": { "status": "happy" }
          }
        }
      },
      "diagnostics": [
        {
            "label": "E3Client",
            "data": {
              ...payloadOfDiagnostic,
              // eg
              "decryption_err": "...."
            }
        }
      ]
    }
  }
}