Metrics improvements

[sbueringer]

This is an umbrella issue to (try) to keep an overview over current feature requests and limitations around metrics:

Misc:

• Support OpenTelemetry for metrics on top of Prometheus #305

Related to global registry, registration on init, ...:

• Remove metrics global registry #210
• Add a new metrics to indicates the the current queue length. #1969
• Don't set global workqueue MetricsProvider #2238
• metrics.init() method calls metrics.Register() of client-go, cause other component can not observe metrics of client-go #2957
  • upstream k/k issue: Sync.Once in client-go metrics play badly with components that want to provide them by default kubernetes/kubernetes#127739
• Support users options to export go schedule related runtime metrics #2892
• ✨Expose RegisterClientMetrics to register other clien… #2936
• ✨ Support RateLimiterLatency & RequestLatency for client-go metrics (client, workqueue, reflector). #2986
• Support custom metrics provider for controller_runtime metrics #3094

probably more ...

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/lifecycle stale

[sbueringer]

/remove-lifecycle stale
/lifecycle frozen