chore: Add support for ZGC generational memory pools (#566)

Author: bric3

src/main/resources/org/datadog/jmxfetch/default-jmx-metrics.yaml

@@ -133,6 +133,14 @@
       Usage.used:
         alias: jvm.gc.eden_size
         metric_type: gauge
+- include:
+    domain: java.lang
+    type: MemoryPool
+    name: ZGC Young Generation
+    attribute:
+      Usage.used:
+        alias: jvm.gc.eden_size
+        metric_type: gauge
 - include:
     domain: java.lang
     type: MemoryPool
@@ -189,6 +197,14 @@
       Usage.used:
         alias: jvm.gc.old_gen_size
         metric_type: gauge
+- include:
+    domain: java.lang
+    type: MemoryPool
+    name: ZGC Old Generation
+    attribute:
+      Usage.used:
+        alias: jvm.gc.old_gen_size
+        metric_type: gauge
 - include:
     domain: java.lang
     type: MemoryPool
@@ -204,4 +220,4 @@
     attribute:
       Usage.used:
         alias: jvm.gc.metaspace_size
-        metric_type: gauge
+        metric_type: gauge