Attempt generational storage of capture metrics (#1125)

### What does this PR do?

This commit attempts the generational storage of metrics in the capture
recorder. I am patterning this work from metrics-prometheus-exporter and
I think I understand how this is wired up?

One thing of note gauges are now ints and not f64s although the interface
still requires f64 on the gauge! side. Unsure how that works out.

Author: blt

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - logrotate_fs is now behind a feature flag and not enabled in the default
   build. It remains enabled in the release artifact.
 - The build now includes http1 and http2 support. Actual usage and availability may vary.
+- Metrics storage is now generational, expiring unwritten metrics every 3 seconds.
 
 ## [0.24.0]
 ## Added