feat(container): auto-tune JVM GC algorithm in setenv.sh based on available vCPUs (#36259)

## Summary

- Replaces the static `JAVA_OPTS_MEMORY` GC config with CPU-aware
auto-selection at container startup
- 1–3 vCPUs → G1GC (default) + `G1PeriodicGCInterval=10000` to return
memory to OS on idle
- 4+ vCPUs → `-XX:+UseZGC` (Java 25 GenerationalZGC by default;
sub-millisecond pauses, scales with cores)
- SerialGC explicitly excluded — not appropriate for a long-running
multi-threaded web server

## Details

CPU detection uses `nproc` with `/proc/cpuinfo` fallback; defaults to 2
if neither is available. Base memory flags (`MaxRAMPercentage=72.0`,
heap free ratios, NIO buffer cap) are unchanged. Set `JAVA_OPTS_MEMORY`
before startup to bypass auto-selection entirely.

Follows the same cgroup-aware pattern already used by
`JAVA_OPTS_DIRECT`.

## Test plan

- [ ] Verify startup log prints `setenv: auto-GC: ...` with detected
vCPU count
- [ ] On a 1-vCPU container (or `nproc` returning 1–3), confirm
`G1PeriodicGCInterval` appears in JVM flags (`-XX:+PrintFlagsFinal` or
`jcmd <pid> VM.flags`)
- [ ] On a 4+-vCPU container, confirm `-XX:+UseZGC` / GenerationalZGC is
active
- [ ] Set `JAVA_OPTS_MEMORY="-XX:MaxRAMPercentage=60.0"` and confirm
auto-tune block is skipped
- [ ] Confirm no regression in startup time or heap usage on standard
containers

Closes #36258

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: wezell

dotCMS/src/main/resources/container/tomcat9/bin/setenv.sh

@@ -5,8 +5,23 @@ export LANG=${LANG:-"C.UTF-8"}
 
 export JAVA_OPTS_BASE=${JAVA_OPTS_BASE:-"-Djava.awt.headless=true  -Djava.library.path=/usr/lib/$( uname -m )-linux-gnu/ -XX:+UseCompactObjectHeaders --enable-preview "}
 
-# This is what MS jaz always runs. G1GC is now java default
-export JAVA_OPTS_MEMORY=${JAVA_OPTS_MEMORY:-"-XX:MaxRAMPercentage=72.0 -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=50 -XX:G1PeriodicGCInterval=10000 -Djdk.nio.maxCachedBufferSize=262144"}
+# Auto-tune GC algorithm based on available vCPUs:
+#   1-3 cores → G1GC (default) + G1PeriodicGCInterval to return memory to OS on idle
+#   4+        → ZGC  (Java 25 uses GenerationalZGC by default; sub-ms pauses, scales with cores)
+# Override by setting JAVA_OPTS_MEMORY before this script runs.
+if [ -z "${JAVA_OPTS_MEMORY+set}" ]; then
+  _cpus=$(nproc 2>/dev/null || grep -c '^processor' /proc/cpuinfo 2>/dev/null || echo 2)
+  _mem_base="-XX:MaxRAMPercentage=72.0 -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=50 -Djdk.nio.maxCachedBufferSize=262144"
+
+  if [ "$_cpus" -le 3 ]; then
+    _gc="-XX:G1PeriodicGCInterval=10000"
+  else
+    _gc="-XX:+UseZGC"
+  fi
+
+  export JAVA_OPTS_MEMORY="$_mem_base $_gc"
+  echo "setenv: auto-GC: ${_gc} (${_cpus} vCPU; override via JAVA_OPTS_MEMORY)"
+fi
 
 # Calculate direct (off-heap) buffer memory based on container memory to prevent unbound growth 
 # can't use a percentage here so we have to calc it ourselves