refactor: Fix request type definition

We now distinguish between the callback variant and the promise

src/lib/request/index.ts

@@ -4,10 +4,17 @@ import { MetricsCollector } from '../metrics';
 import * as needle from 'needle';
 
 // A hybrid async function: both returns a promise and takes a callback
-export = async (
+async function requestWrapper(
+  payload: any,
+): Promise<{ res: needle.NeedleResponse; body: any }>;
+async function requestWrapper(
+  payload: any,
+  callback: (err: Error | null, res?, body?) => void,
+): Promise<void>;
+async function requestWrapper(
   payload: any,
   callback?: (err: Error | null, res?, body?) => void,
-): Promise<void | { res: needle.NeedleResponse; body: any }> => {
+): Promise<void | { res: needle.NeedleResponse; body: any }> {
   const totalNetworkTimeTimer = MetricsCollector.NETWORK_TIME.createInstance();
   totalNetworkTimeTimer.start();
   try {
@@ -28,4 +35,6 @@ export = async (
   } finally {
     totalNetworkTimeTimer.stop();
   }
-};
+}
+
+export = requestWrapper;