Feat/manual payment (#318)

What
A dummy payment provider for testing and potentially other relevant use cases like accepting cash payments. Also makes it possible to start server without notification/payment/fulfillment providers.

Why
When setting up a starter project it introduces unnecessary overhead to have to set up an account with a payment provider (e.g. Stripe). Adding a dummy provider will remove friction.

How
Extremely simple wrapper functionality.

packages/medusa-payment-manual/.prettierrc

@@ -0,0 +1,7 @@
+{
+  "endOfLine": "lf",
+  "semi": false,
+  "singleQuote": false,
+  "tabWidth": 2,
+  "trailingComma": "es5"
+}