Add description of new task features

docs/tasks/activities/index.adoc

@@ -108,10 +108,63 @@ of each other.
 
 #TODO#
 
-== Migration from 4.3 and before
+== Migration from 4.3 and Before
 
 #TODO#
 
-== GUI support
+== GUI Support
 
 #TODO#
+
+== New Features
+
+=== Cluster Auto-Scaling Capability
+
+Distributed - a.k.a. multi-node - activities can be scaled up or down by starting or stopping worker tasks.
+This scaling is appropriate when the distribution definition changes, e.g. number of worker tasks is increased
+or decreased. It should be done also when the cluster configuration changes, e.g. nodes are added or deleted.
+
+This up/down-scaling was present in midPoint since 3.8 (as an experimental feature) in the form of _workers
+reconciliation_ process. In 4.4 the following changes were done:
+
+1. The workers reconciliation process was improved and fixed:
+ - It no longer closes superfluous workers - it suspends them instead, allowing resuming them when needed.
+ - When suspending the workers, any unprocessed buckets are returned to the coordinator to process them
+immediately by other workers. The same is true when the task stops for any other reason.
+This eliminates lengthy "scavenging" process at the end of the processing.
+ - When in scavenging phase, non-scavenger workers are not created. Only the scavengers are.
+ - The whole reconciliation is now driven by node.operationalState (i.e. from repo) instead of
+node.executionState (determined dynamically). So in case of unstable clusters or transition situations
+the results should be more predictable.
+
+2. New auto-scaling activity was created. It periodically scans for tasks that are autoscaling-enabled
+and invokes workers reconciliation process on them, if the cluster state has changed in the meanwhile.
+(Note that we currently do not support auto-scaling triggered by changes in activity distribution
+definition. The user is responsible for reconciling the workers manually in that cases.)
+
+=== Cluster-wide Thresholds
+
+The xref:/midpoint/reference/tasks/thresholds/[threshold mechanism] before 4.4 was limited to a single node,
+and the related policy rules counters were transient, so they did not survive midPoint node restarts.
+There were other limitations as well.
+
+Starting with 4.4, counters for policy rules are stored persistently in the respective task objects,
+providing support for cluster-wide watching of policy rules thresholds, across task and node restarts.
+
+=== Task Statistics Improvements
+
+* Flexible xref:reporting/execution-reports/[activity reports] were introduced:
+
+- buckets processed,
+- items processed,
+- ConnId operations executed,
+- internal operations executed.
+
+Also, bucket size analysis mode is now available. It allows determining size of buckets before
+real processing starts: either all buckets, or a (random or regular) sample of specified size.
+
+* The following information is now collected per individual activities (not per tasks):
+
+- synchronization statistics,
+- actions executed,
+- work bucket management statistics.