Enable routing data to different data streams

[felixbarny]

We'd like to allow users to use a reroute processor to send APM data to arbitrary namespaces. Currently, when using a Fleet-managed APM Server, sending data to a different data stream using the reroute process isn't possible. That's because the API Key permissions are very narrow and only allow sending data to an exact data stream.

Similarly to what we've done for some other integrations where we want to allow routing (see elastic/integrations#6340), we just need to add the elasticsearch.dynamic_dataset: true and elasticsearch.dynamic_namespace: true flags, accordingly.

I'm proposing to add elasticsearch.dynamic_namespace: true to all data streams and to add elasticsearch.dynamic_dataset: true only to the app_metrics and app_logs data streams. That's because changing the data set for other data stream, such as internal_metrics could confuse the APM UI. If required, we can always add elasticsearch.dynamic_dataset: true to other data streams, such as the traces data stream.

[felixbarny]

One caveat for allowing routing to different datasets for custom metrics is that the target data streams need to have to have the dynamic templates and ingest processors that are used in the metrics-apm.app_metrics-* data stream.