feature request: Forward Pi-Hole Logs to Splunk

[klutchell]

• https://forums.balena.io/t/balena-pi-hole-query-logs-to-splunk/354330/2
• https://satiex.net/infosec/guides/forward-pi-hole-logs-to-splunk/

It looks like we would need to add several things to the project, including but not limited to:

1. the splunk binary for ARM, or whichever platform we are targeting
2. inputs and outputs config files for splunk
3. install any splunk dependencies
4. set the splunkforwarder to start on container start, after Pi-hole

A better plan might be to run the splunk forwarder as it's own container, to avoid conflicting with the Pi-hole installation and dependencies. We could put the logs on a shared volume or something like that.
https://docs.splunk.com/Documentation/Forwarder/8.2.5/Forwarder/DeployandrunauniversalforwarderinsideaDockercontainer

Putting this here for consideration, and looking for interest and/or volunteers.