Clarify behavior of custom launcher JVM opts

[pkoenig10]

The README suggests that JVM opts from launcher-custom.yml "override" JVM options from launcher-static.yml, but this is not the case. The JVM options are concatenated.

The only other modifications we make to the JVM options are for container support.

go-java-launcher/launchlib/launcher.go

Lines 100 to 104 in 02b02da

	var combinedJvmOpts []string
	combinedJvmOpts = append(combinedJvmOpts, staticConfig.JavaConfig.JvmOpts...)
	combinedJvmOpts = append(combinedJvmOpts, customConfig.JvmOpts...)
	jvmOpts := createJvmOpts(combinedJvmOpts, customConfig, logger)

go-java-launcher/launchlib/launcher.go

Lines 281 to 308 in 02b02da

	func createJvmOpts(combinedJvmOpts []string, customConfig *CustomLauncherConfig, logger io.WriteCloser) []string {
	if isEnvVarSet("CONTAINER") && !customConfig.DisableContainerSupport && !hasMaxRAMOverride(combinedJvmOpts) {
	_, _ = fmt.Fprintln(logger, "Container support enabled")
	jvmOptsWithUpdatedHeapSizeArgs, err := filterHeapSizeArgsV2(combinedJvmOpts)
	if err != nil {
	// When we fail to get the memory limit from the cgroups files, fallback to using percentage-based heap
	// sizing. While this method doesn't take into account the per-processor memory offset, it is supported
	// by all platforms using Java.
	// Also, when the memory limit is unusually high (defined to be over 1TB), we revert to the
	// percentage-based heap sizing. This is to handle the edge case where the cgroups memory limit is set
	// to be an arbitrary large value.
	combinedJvmOpts = filterHeapSizeArgs(combinedJvmOpts)
	} else {
	combinedJvmOpts = jvmOptsWithUpdatedHeapSizeArgs
	}
	return combinedJvmOpts
	}
	if isEnvVarSet("CONTAINER") {
	if customConfig.DisableContainerSupport {
	_, _ = fmt.Fprintln(logger, "Container support disabled in launcher-custom.yml")
	} else if hasMaxRAMOverride(combinedJvmOpts) {
	_, _ = fmt.Fprintln(logger, "Container support disabled: -XX:MaxRAM override present")
	}
	}
	return combinedJvmOpts
	}