Updated graphql-from-node examples to be amplify mock compatible (#4441)

* Fix "Must provide Source" error

Without Content Type header local mock is failing with "Must Provice Source"

* Amplify mock commonjs note

Added a note stating that the proposed functions written in ES module syntax are not supported by amplify mock. Removed wrongly referenced 'variables' in one of the examples.

* Added callout to use node-fetch v2 for cjs

* reverse order of http headers in last example

* Remove wrong comma in doc's example

* Update src/fragments/lib/graphqlapi/graphql-from-node.mdx

Co-authored-by: josef <[email protected]>

* commit to re-trigger checks

---------

Co-authored-by: josef <[email protected]>
Co-authored-by: Katie Goines <[email protected]>

Author: 3 people

src/fragments/lib/graphqlapi/graphql-from-node.mdx

@@ -1,5 +1,5 @@
 You can call an AppSync GraphQL API from a Node.js app or a Lambda function. Take a basic `Todo` app as an example:
-
+ 
 ```graphql
 type Todo @model @auth(rules: [{ allow: public }]) {
   name: String
@@ -150,9 +150,10 @@ export const handler = async (event) => {
   const options = {
     method: 'POST',
     headers: {
-      'x-api-key': GRAPHQL_API_KEY
+      'x-api-key': GRAPHQL_API_KEY,
+      'Content-Type': 'application/json'
     },
-    body: JSON.stringify({ query, variables })
+    body: JSON.stringify({ query })
   };
 
   const request = new Request(GRAPHQL_ENDPOINT, options);
@@ -222,7 +223,8 @@ export const handler = async (event) => {
   const options = {
     method: 'POST',
     headers: {
-      'x-api-key': GRAPHQL_API_KEY
+      'x-api-key': GRAPHQL_API_KEY,
+      'Content-Type': 'application/json'
     },
     body: JSON.stringify({ query, variables })
   };