feat(plugins): Adds add-on plugin

Adds an add-on plugin, that supports adding add-ons to line items in the cart

packages/medusa-plugin-add-ons/src/models/__mocks__/add-on.js

@@ -0,0 +1,46 @@
+import { IdMap } from "medusa-test-utils"
+
+export const addOns = {
+  testAddOn: {
+    _id: IdMap.getId("test-add-on"),
+    name: "Chili",
+    prices: [
+      {
+        currency_code: "DKK",
+        amount: 20,
+      },
+    ],
+    valid_for: [IdMap.getId("test-product")],
+  },
+  testAddOn2: {
+    _id: IdMap.getId("test-add-on-2"),
+    name: "Chili",
+    prices: [
+      {
+        currency_code: "DKK",
+        amount: 20,
+      },
+    ],
+    valid_for: [IdMap.getId("test-product")],
+  },
+}
+
+export const AddOnModelMock = {
+  create: jest.fn().mockReturnValue(Promise.resolve()),
+  find: jest.fn().mockImplementation((query) => {
+    return Promise.resolve([addOns.testAddOn, addOns.testAddOn2])
+  }),
+  updateOne: jest.fn().mockImplementation((query, update) => {
+    return Promise.resolve()
+  }),
+  deleteOne: jest.fn().mockReturnValue(Promise.resolve()),
+  findOne: jest.fn().mockImplementation((query) => {
+    if (query._id === IdMap.getId("test-add-on")) {
+      return Promise.resolve(addOns.testAddOn)
+    }
+    if (query._id === IdMap.getId("test-add-on-2")) {
+      return Promise.resolve(addOns.testAddOn2)
+    }
+    return Promise.resolve(undefined)
+  }),
+}

packages/medusa-plugin-add-ons/src/models/add-on.js

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+import mongoose from "mongoose"
+import { BaseModel } from "medusa-interfaces"
+
+class AddOnModel extends BaseModel {
+  static modelName = "AddOn"
+  static schema = {
+    name: { type: String, required: true },
+    prices: { type: [], required: true },
+    // Valid products
+    valid_for: { type: [String], required: true },
+    metadata: { type: mongoose.Schema.Types.Mixed, default: {} },
+  }
+}
+
+export default AddOnModel