Adding profiling option to checkVec task (elastic#129502)

Adds simple profiling to checkVec.

```
DO_PROFILING=true ./gradlew :qa:vector:checkVec --args=/path/to/config.json
```

Author: benwtrent

qa/vector/build.gradle

@@ -42,9 +42,12 @@ tasks.register("checkVec", JavaExec) {
   systemProperty "es.logger.out", "console"
   systemProperty "es.logger.level", "INFO"  // Change to DEBUG if needed
   systemProperty 'es.nativelibs.path', TestUtil.getTestLibraryPath(file("../../libs/native/libraries/build/platform/").toString())
-
+  jvmArgs '-Xms4g', '-Xmx4g', '-Djava.util.concurrent.ForkJoinPool.common.parallelism=8', '-XX:+UnlockDiagnosticVMOptions', '-XX:+DebugNonSafepoints', '-XX:+HeapDumpOnOutOfMemoryError'
   if (buildParams.getRuntimeJavaVersion().map { it.majorVersion.toInteger() }.get() >= 21) {
-    jvmArgs '-Xms4g', '-Xmx4g', '--add-modules=jdk.incubator.vector', '--enable-native-access=ALL-UNNAMED', '-Djava.util.concurrent.ForkJoinPool.common.parallelism=8', '-XX:+UnlockDiagnosticVMOptions', '-XX:+DebugNonSafepoints', '-XX:+HeapDumpOnOutOfMemoryError'
+    jvmArgs '--add-modules=jdk.incubator.vector', '--enable-native-access=ALL-UNNAMED'
+  }
+  if (System.getenv("DO_PROFILING") != null) {
+    jvmArgs '-XX:StartFlightRecording=dumponexit=true,maxsize=250M,filename=knn.jfr,settings=profile.jfc'
   }
 }