Metric to monitor the expiration time of certificates

[benshalev849]

Describe the solution you'd like
A metric produced by the NGINX Ingress Controller, similar to the k8s native one: nginx_ingress_controller_ssl-expire that shows the expiration time and other certificate related metrics.

Additional context
In the NGINX Ingress Controller of k8s there are many metrics for certificates and dashboards, most importantly the expiration of the certificates, we think this is a good metric that can be added to the F5 official NGINX Ingress Controller too.

[github-actions]

Hi @benshalev849 thanks for reporting!

Be sure to check out the docs and the Contributing Guidelines while you wait for a human to take a look at this 🙂

Cheers!

[haywoodsh]

The NGINX API does not seem to provide information we need on cert expiry. We will need to look into how this metric should be implemented, and determine whether we need to submit a future request to NGINX itself or incorporate this into the Ingress Controller ourselves.