Add a quantity field to the item create modal form. (#615)

* Add a quantity field to the item create modal form.

* Fix prettier code format complaint.

* Update en.json allowing the label of the field to be translated.

* Including changes generated by swag and typescript-types tasks.

* Fixed tests, item duplication and lint errors.

* Fix linter issues again and an error introduced in 912e5b2

* Fixed a test that creates an item through the go:coverage task

backend/app/api/static/docs/docs.go

@@ -2241,6 +2241,9 @@ const docTemplate = `{
                 "parentId": {
                     "type": "string",
                     "x-nullable": true
+                },
+                "quantity": {
+                    "type": "integer"
                 }
             }
         },
@@ -2466,6 +2469,10 @@ const docTemplate = `{
                 "quantity": {
                     "type": "integer"
                 },
+                "soldTime": {
+                    "description": "Sale details",
+                    "type": "string"
+                },
                 "updatedAt": {
                     "type": "string"
                 }