Adding custom fields is not working

[artyombaranovskiytr]

The latest beats API provides the ability to add custom fields to result docs via configuration,
However it doesn't work in wmibeat (likely, some other call to libbeat API is required in either Setup or Config step).

This is required to pass static environment parameters known at deployment time, e.g.:
shipper:
fields_under_root: true
fields:
instance: "Monitored Instance"
host: "Monitored Host"

Could you please look into this?

Best regards,
Artsiom