MM-60283 Add standard response and API docs to /client_perf API (#28124)

* MM-60283 Add standard response to /client_perf API

* Add API docs for /client_perf endpoint

* Fix invalid response schema

server/channels/api4/metrics.go

@@ -35,4 +35,6 @@ func submitPerformanceReport(c *Context, w http.ResponseWriter, r *http.Request)
 		c.Err = appErr
 		return
 	}
+
+	ReturnStatusOK(w)
 }