Metrics exposed about certificate expiration can become stale

[dadrus]

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• I agree to follow this project's Code of Conduct.
• I have read and am following this repository's Contribution Guidelines."
• I could not find a solution in the existing issues, docs, nor discussions.

Describe the bug

The PRs #1230 and #1232 have introduced hot reloading of the key stores to allow key rotation without downtimes. Unfortunately, it has been forgotten to update the implementation related to the exposure of certificate expiration metrics. This way, even if the certificates have been rotated, the expiration information of old certificates is still exposed.

How can the bug be reproduced

1. Start heimdall e.g. in decision with TLS enabled and metrics exposed
2. Check the certificate expiration metrics
3. Updated the key store used for TLS with a new key material and certificate
4. Check the certificate expiration metrics. It is the old one

Relevant log output

No response

Relevant configuration

No response

Version

v0.14.3-alpha

On which operating system are you observing this issue?

Linux

In which environment are you deploying?

Docker

Additional Context

No response