Support LogModel in mlflow-go

This is experimental API from MLFlow comments:

// .. note::
  //     Experimental: This API may change or be removed in a future release without warning.
  rpc logModel (LogModel) returns (LogModel.Response) {
    option (rpc) = {
      endpoints: [{
        method: "POST",
        path: "/mlflow/runs/log-model"
        since { major: 2, minor: 0 },
      }],
      visibility: PUBLIC,
      rpc_doc_title: "Log Model",
    };
  }

do we even need to support if right now or we cal left it for community?

mlflow / mlflow-go

Support LogModel in mlflow-go #24