hello TypeScript: Define type of req object

Make it clearer that `req` is a CDS `Request` object.

hello/srv/world.ts

@@ -1,5 +1,7 @@
+import { Request } from "@sap/cds/apis/services"
+
 module.exports = class say {
-    hello(req: any) {
+    hello(req: Request) {
         return `Hello ${req.data.to} from a TypeScript file!`
     }
 }