feat(medusa): cart context (#201)

- Adds a context field to Cart
- context is automatically populated with ip + user agent
- context can be updated via POST /store/cart/:id or set when creating via POST /store/cart

integration-tests/api/__tests__/store/cart.js

@@ -72,6 +72,26 @@ describe("/store/carts", () => {
       const getRes = await api.post(`/store/carts/${response.data.cart.id}`);
       expect(getRes.status).toEqual(200);
     });
+
+    it("creates a cart with context", async () => {
+      const api = useApi();
+      const response = await api.post("/store/carts", {
+        context: {
+          test_id: "test",
+        },
+      });
+      expect(response.status).toEqual(200);
+
+      const getRes = await api.post(`/store/carts/${response.data.cart.id}`);
+      expect(getRes.status).toEqual(200);
+
+      const cart = getRes.data.cart;
+      expect(cart.context).toEqual({
+        ip: "::ffff:127.0.0.1",
+        user_agent: "axios/0.21.1",
+        test_id: "test",
+      });
+    });
   });
 
   describe("POST /store/carts/:id", () => {