feat(js): expose current apiKey on the client instance

This is good for instantiating other information (like insights client) and is consistent with the appId being exposed.

Author: Haroenv

templates/javascript/clients/api-single.mustache

@@ -47,6 +47,11 @@ export function create{{#lambda.titlecase}}{{clientName}}{{/lambda.titlecase}}({
      */
     appId: appIdOption,
 
+    /**
+      * The `apiKey` currently in use.
+      */
+    apiKey: apiKeyOption,
+
     /**
      * Clears the cache of the transporter for the `requestsCache` and `responsesCache` properties.
      */
@@ -177,4 +182,4 @@ export function create{{#lambda.titlecase}}{{clientName}}{{/lambda.titlecase}}({
   };
 }
 
-{{/operations}}
+{{/operations}}