fix: better logging docs

Author: razvan

docs/modules/spark-k8s/pages/usage-guide/logging.adoc

@@ -1,5 +1,8 @@
 = Logging
 
-Logs produced by SparkApplications are automatically collected by vector agents and can be aggregated as described in xref:concepts:logging.adoc[roles]
+The Spark operator installs a https://vector.dev/docs/setup/deployment/roles/#agent[vector agent] as a side-car container in every application Pod except the `job` Pod that runs `spark-submit`. It also configures the logging framework to output logs in XML format. This is the same https://logging.apache.org/log4j/2.x/manual/layouts.html#XMLLayout[format] used across all Stackable products and it enables the https://vector.dev/docs/setup/deployment/roles/#aggregator[vector aggregator] to collect  logs across the entire platform.
+
+It is the user's responsibility to install and configure the vector aggregator, but the agents can discover the aggregator automatically using a discovery ConfigMap as described in the xref:concepts:logging.adoc[logging concepts]. 
 
 NOTE: Only logs produced by the application's driver and executors are collected. Logs produced by `spark-submit` are discarded.
+