Add subject+expiry dates to certificates in kubernetes.io/tls secrets

[tstenner]

Is your feature request related to a problem? Please describe.

TLS keys/certificates are opaque, but the central information (validity dates, subject) is often needed when troubleshooting connection issues.

A clear and concise description of what the problem is.

Describe the solution you'd like

Certificates in secrets of type kubernetes.io/tls should show the subjects and expiry dates in the overview.

Describe alternatives you've considered

Copying the entire secret, extracting the pem blocks and getting a summary with openssl/kse is possible, but not user friendly.

A plugin like kubectl get secret … -oyaml| yq -r .["tls.key"] | openssl x509 … could work, but go has all of these functions already in the stdlib.