docs: fixes to API and JS SDK references (#13795)

www/apps/api-reference/specs/admin/code_samples/JavaScript/admin_refund-reasons/post.js

@@ -9,7 +9,7 @@ export const sdk = new Medusa({
 })
 
 sdk.admin.refundReason.create({
-  value: "refund",
+  code: "refund",
   label: "Refund",
 })
 .then(({ refund_reason }) => {

www/apps/api-reference/specs/admin/code_samples/JavaScript/admin_refund-reasons_{id}/post.js

@@ -9,7 +9,7 @@ export const sdk = new Medusa({
 })
 
 sdk.admin.refundReason.update("ret_123", {
-  value: "refund",
+  code: "refund",
   label: "Refund",
 })
 .then(({ refund_reason }) => {

www/apps/api-reference/specs/admin/code_samples/Shell/admin_refund-reasons/post.sh

@@ -3,5 +3,6 @@ curl -X POST '{backend_url}/admin/refund-reasons' \
 -H 'Content-Type: application/json' \
 --data-raw '{
   "label": "{value}",
+  "code": "{value}",
   "description": "{value}"
 }'