forwarding workflow logs to loki via promtail

[andybrown668]

I run ARC in kubernetes and have a promtail daemonset that successfully scrapes controller and runner logs.
But, I don't see an easy way to scrape workflow logs.

I can see they're stored in /runner/_diag/pages/*.log and I could mount that as a hostpath volume so promtail could scrape.
But I need to have workflow run-id and run-attempt to make the log useful.

It feels deliberate that the workflow run logs don't end up on the runner stdout/stderr with a workflow run-id prefix - but that's where it'd be easiest to scrape them from...