Support host and service templates to send variables to Elasticsearch

[wols]

It would be great if we could select host.vars and service.vars additional sent to Elasticsearch using the ElastichsearchWriter. The idea was inspired by #6213.

This should follow the template logic of InfluxdbWriter:

object ElasticsearchWriter "elasticsearch" {
  # other options...

  host_template = {
    tags = {
      location = "$host.vars.geodata$"
    }
  }
  service_template = {
    tags = {
      snmp_oid = "$service.vars.snmpv3_oid$"
    }
  }
}

See also Tags vs Fields

[dnsmichi]

tags is an additional JSON field in the data written for each event type then? This may have the same effect as with performance metrics, too much data.

[lippserd]

Unfortunately there are no plans to implement this at moment. If you're still interested in this feature, please contact us via https://icinga.com for sponsoring.

[ngoeddel-openi]

Since we also need this feature now we are working on implementing this in a fork and want to create a pull request if we are ready.