docs: adds tutorial (#323)

* docs: adds installation guide for tutorial

* docs: adds creating your medusa server guide

* add quick starter

* rename to reflect docker usage

* docs: adds custom functionality tutorial

* docs: adds linking with medusa cloud

* fix: PR

Co-authored-by: olivermrbl <oliver@mrbltech.com>

packages/medusa/src/services/cart.js

@@ -694,6 +694,10 @@ class CartService extends BaseService {
         }
       }
 
+      if ("metadata" in update) {
+        cart.metadata = this.setMetadata_(cart, update.metadata)
+      }
+
       if ("context" in update) {
         const prevContext = cart.context || {}
         cart.context = {