Add number of workers/batch_size... at node level

[arnaudlemaignen]

Hi all

there are important metrics which are available at node level and deserved to be output to this exporter.
See in bold below
this is from a logstash 5

curl -XGET 'localhost:9600/_node'
{"host":"logstash-18-05ptr","version":"5.6.16","http_address":"0.0.0.0:9600","id":"167ab0da-596d-4b2c-b642-7369ce457f0a","name":"eaa-platform-logstash-18-05ptr","pipeline":{"workers":8,"batch_size":125,"batch_delay":5,"config_reload_automatic":true,"config_reload_interval":3,"dead_letter_queue_enabled":false,"id":"main"},"os":{"name":"Linux","arch":"amd64","version":"3.10.0-862.29.1.el7.x86_64","available_processors":8},"jvm":{"pid":1,"version":"1.8.0_252","vm_version":"1.8.0_252","vm_vendor":"Oracle Corporation","vm_name":"OpenJDK 64-Bit Server VM","start_time_in_millis":1598427774383,"mem":{"heap_init_in_bytes":8589934592,"heap_max_in_bytes":8520204288,"non_heap_init_in_bytes":2555904,"non_heap_max_in_bytes":0},"gc_collectors":["ParNew","ConcurrentMarkSweep"]}}

Can this be added in the logstash_info_node as labels or elsewhere?
tks