Update aws-config.json

https://aws.amazon.com/blogs/security/get-the-full-benefits-of-imdsv2-and-disable-imdsv1-across-your-aws-infrastructure/
```
"MetadataOptions": {
                        "State": "applied", 
                        "HttpEndpoint": "enabled", 
                        "HttpTokens": "optional", 
                        "HttpPutResponseHopLimit": 1
                    },
```

rule-packs/aws-config.json

@@ -1110,5 +1110,17 @@
       }
     ],
     "alertLevel": "MEDIUM"
+  },
+  {
+    "name": "ec2-imdsv2-optional",
+    "description": "Checks if an Amazon EC2 Instances have been configured to no require Instance Metadata Service Version 2 (IMDSv2)",
+    "queries": [
+      {
+        "name": "query0",
+        "query": "find aws_instance with httpTokens = 'optional' and httpEndpointEnabled=true",
+        "version": "v1"
+      }
+    ],
+    "alertLevel": "MEDIUM"
   }
 ]