[plugin-jvm] add metrics of concurrent garbage collection
[plugin-jvm] add metrics of concurrent garbage collection

hiroakis/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,hiroakis/mackerel-agent-plugins,hiroakis/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,hiroakis/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins