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/src/services/manual-payment.js

@@ -0,0 +1,95 @@
+import { PaymentService } from "medusa-interfaces"
+
+class ManualPaymentService extends PaymentService {
+  static identifier = "manual"
+
+  constructor() {
+    super()
+  }
+
+  /**
+   * Returns the currently held status.
+   * @param {object} paymentData - payment method data from cart
+   * @returns {string} the status of the payment
+   */
+  async getStatus(paymentData) {
+    const { status } = paymentData
+    return status
+  }
+
+  /**
+   * Creates a manual payment with status "pending"
+   * @param {object} cart - cart to create a payment for
+   * @returns {object} an object with staus
+   */
+  async createPayment() {
+    return { status: "pending" }
+  }
+
+  /**
+   * Retrieves payment
+   * @param {object} data - the data of the payment to retrieve
+   * @returns {Promise<object>} returns data
+   */
+  async retrievePayment(data) {
+    return data
+  }
+
+  /**
+   * Updates the payment status to authorized
+   * @returns {Promise<{ status: string, data: object }>} result with data and status
+   */
+  async authorizePayment() {
+    return { status: "authorized", data: { status: "authorized" } }
+  }
+
+  /**
+   * Noop, simply returns existing data.
+   * @param {object} sessionData - payment session data.
+   * @returns {object} same data
+   */
+  async updatePayment(sessionData) {
+    return sessionData.data
+  }
+
+  async deletePayment() {
+    return
+  }
+
+  /**
+   * Updates the payment status to captured
+   * @param {object} paymentData - payment method data from cart
+   * @returns {object} object with updated status
+   */
+  async capturePayment() {
+    return { status: "captured" }
+  }
+
+  /**
+   * Returns the data currently held in a status
+   * @param {object} paymentData - payment method data from cart
+   * @returns {object} the current data
+   */
+  async getPaymentData(session) {
+    return session.data
+  }
+
+  /**
+   * Noop, resolves to allow manual refunds.
+   * @param {object} payment - payment method data from cart
+   * @returns {string} same data
+   */
+  async refundPayment(payment) {
+    return payment.data
+  }
+
+  /**
+   * Updates the payment status to cancled
+   * @returns {object} object with canceled status
+   */
+  async cancelPayment() {
+    return { status: "canceled" }
+  }
+}
+
+export default ManualPaymentService