Proof of concept index metrics tracker.

[tpendragon]

This is nowhere near complete, but it's a nice proof of concept for time to poll as defined in #115

The :monotonic_time stuff is pulled from Telemetry's recommendations: https://hexdocs.pm/telemetry/readme.html

[github-actions]

Container Scanning Status: ✅ Success

ghcr.io/pulibrary/dpul-collections:pr-153 (debian 12.6)
=======================================================
Total: 0 (HIGH: 0, CRITICAL: 0)

[hackartisan]

This is looking good. Do you think we shouldn't use a span, then?

[hackartisan]

Like using https://hexdocs.pm/opentelemetry_api/OpenTelemetry.Tracer.html#start_span/2

[tpendragon]

Like using https://hexdocs.pm/opentelemetry_api/OpenTelemetry.Tracer.html#start_span/2

I looked at that, but I couldn't figure out how to wrap something around a process that happens over a long period of time. Like I guess I could spawn a task that spins and waits...but I think just sending an event for the duration is just as good.