Fix elasticsearch output adding bulk index item

[leehinman]

Error:

{"log.level":"debug","@timestamp":"2023-02-21T21:16:52.852Z","log.logger":"elasticsearch-output","log.origin":{"file.name":"elasticsearch/output.go","file.line":137},"message":"Failed to add items: \"\"","service.name":"shipper","ecs.version":"1.6.0"}

most likely due to b5bdbfe, was working at 4d8899c

[leehinman]

When fixing the event should go to the correct index not the default "elastic-agent-shipper-test" index