Update GraphQL DuoChat docs

This MR updates the DuoChat GraphQL Docs.

It removes some outdated information and removes GraphQL Query variables that are no longer needed.

doc/development/ai_features/duo_chat.md

@@ -419,7+419,7 @@
           return {
             aiAction: 'CHAT',
             userId, // for example "gid://gitlab/User/1"
             clientSubscriptionId // randomly generated identifier for every message
             htmlResponse: false, // important to bypass HTML processing on every chunk
           };
         },
@@ -433,7+433,7 @@
     },
    ```
 
-Please keep in mind that the clientSubscriptionId must be unique for every subscription. Reusing a clientSubscriptionId will cause several unwanted side effects in the subscription responses.
+Please keep in mind that the clientSubscriptionId must be unique for every request. Reusing a clientSubscriptionId will cause several unwanted side effects in the subscription responses.
 
 ### Duo Chat GraphQL queries