Logic to emit metrics for certificate expiration times, to create alerts and dashboards for observability and monitoring

[steffen-karlsson]

This PR provides logic to emit metrics for certificate expiration time in ms. This is for creating alerts and dashboards for observability and monitoring.

Example of a panel in a dashboard in Grafana:

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[steffen-karlsson]

Examples of the metrics from JMX exporter:

[steffen-karlsson]

Hello @rayokota I see that you're a quite frequent committer to this repo, I'd like to hear if possible, your feedback on this suggestion :) Its at least something we're very interested in, in our company for observability and alerting and currently are having a not so nice solution to cater for it.

Thanks,