reduce Compiler Cache size to 100

The reduction from 500 to 100 is based on observations where 06d7f01fd
reduced the number of generated classes by about an order of magnitude
especially on very large pipelines (e.g. from ~600 to ~30).

logstash-core/src/main/java/org/logstash/config/ir/compiler/ComputeStepSyntaxElement.java

@@ -59,7 +59,7 @@ public final class ComputeStepSyntaxElement<T extends Dataset> {
      * across pipelines and workers.
      */
     private static final ConcurrentHashMap<ComputeStepSyntaxElement<?>, Class<? extends Dataset>> CLASS_CACHE
-        = new ConcurrentHashMap<>(500);
+        = new ConcurrentHashMap<>(100);
 
     private static final AtomicLong DATASET_CLASS_INDEX = new AtomicLong(0);