Support echo server to test POST /verify

TL;DR:
- Add common dependencies like Servant, Aeson, Warp, Cors
- Define a POST /verify endpoint for our client to hit
- POST to /verify client-side onSignIn

website/sandbox/learnpianochords/src/server/API.hs

@@ -0,0 +1,15 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeOperators #-}
+--------------------------------------------------------------------------------
+module API where
+--------------------------------------------------------------------------------
+import Data.Text
+import Servant.API
+import Web.Cookie
+
+import qualified Types as T
+--------------------------------------------------------------------------------
+
+type API = "verify"
+           :> ReqBody '[JSON] T.VerifyGoogleSignInRequest
+           :> Post '[JSON] NoContent