Loki is a new message indexer and querier from Grafana Labs. See
https://github.com/grafana/loki for details on Loki.
This change provides the initial message structure to send bulk message
payloads to the Loki Rest endpoint. omhttp, recieved a new bulk message
format called lokirest. Additionally, the plugin relies on the user to
provide the correct "stream" read message format.
A loki template must be json compatible and include a "stream" key of
key value tags, and a values key of an array of 2 element arrays, where
each 2 element array is the unix epoch in nanoseconds followed by an
unstrectured message.
An example:
template(name="array_loki" type="string" string="{\"stream\":{\"host\":\"%HOSTNAME%\",\"facility\":\"%syslogfacility-text%\",\"priority\":\"%syslogpriority-text%\",\"syslogtag\":\"%syslogtag%\"},\"values\": [[ \"%timegenerated:::date-unixtimestamp%000000000\", \"%msg%\" ]]}")
