fix: support custom agent in node http handler (#489)

* feat(node-http-handler): support custom agent

* fix: supply httpHandlerOptions with client.send() instead of httpOptions

* feat: remove Browser&Node handler options interface from types package

Because these interfaces are constructor interface for individual
http handler, they only need to be exposed from its own http handler
package

Author: AllanZhengYP

packages/protocol-http/src/httpHandler.ts

@@ -1,9 +1,9 @@
 import { HttpRequest } from "./httpRequest";
 import { HttpResponse } from "./httpResponse";
-import { RequestHandler, HttpOptions } from "@aws-sdk/types";
+import { RequestHandler, HttpHandlerOptions } from "@aws-sdk/types";
 
 export type HttpHandler = RequestHandler<
   HttpRequest,
   HttpResponse,
-  HttpOptions
+  HttpHandlerOptions
 >;