Sample logs scenario - send to wired streams and classic streams at the same time (#220737)

To be able to better test classic vs. wired streams, this PR expands the
`sample_logs` scenario to send to both of these places.

<img width="1130" alt="Screenshot 2025-05-11 at 10 55 36"
src="https://github.com/user-attachments/assets/0e75c82e-e96c-4f81-abcc-32347cd82d6b"
/>

```
node scripts/synthtrace.js sample_logs --live --kibana=http://elastic:changeme@localhost:5601 --target=http://elastic:changeme@localhost:9200 --liveBucketSize=1000
```

Author: flash1293

src/platform/packages/shared/kbn-apm-synthtrace/src/lib/streams/streams_synthtrace_client.ts

@@ -24,7 +24,7 @@ export class StreamsSynthtraceClient extends SynthtraceEsClient<StreamsDocument>
       ...options,
       pipeline: streamsPipeline(),
     });
-    this.dataStreams = ['logs', 'logs.*'];
+    this.dataStreams = ['logs', 'logs.*', 'logs-generic-default'];
   }
 
   async forkStream(
@@ -86,7 +86,12 @@ function streamsRoutingTransform() {
   return new Transform({
     objectMode: true,
     transform(document: ESDocumentWithOperation<StreamsDocument>, encoding, callback) {
-      document._index = 'logs';
+      // 50-50 send to logs or to logs-generic-default
+      if (Math.random() > 0.5) {
+        document._index = 'logs-generic-default';
+      } else {
+        document._index = 'logs';
+      }
       callback(null, document);
     },
   });