MM-13606 Remove consumeAndClose and clean up integration response handling (#10066)

* MM-13606 Remove consumeAndClose

* Allow overriding HTTPService's request timeout

* MM-13606 Clean up integration response handling

* Properly close httptest servers

* Address feedback

* Only call buf.Bytes when necessary

* Properly check for errors in doOutgoingWebhookRequest

* Add comment explaining ignored ioutil.ReadAll errors

services/httpservice/client_test.go

@@ -139,3 +139,9 @@ func TestUserAgentIsSet(t *testing.T) {
 	}
 	client.Do(req)
 }
+
+func NewHTTPClient(transport http.RoundTripper) *http.Client {
+	return &http.Client{
+		Transport: transport,
+	}
+}