Allow rotation of Signer key material and certificates without being forced to restart heimdall

[dadrus]

Preflight checklist

• I agree to follow this project's Code of Conduct.
• I have read and am following this repository's Contribution Guidelines."
• I have discussed this feature request with the community.

Describe the background of your feature request

As of today, there is a need to restart heimdall each time the Signer key and certificates were updated. This approach is secure and convenient in most cases. There are however cases, e.g. requireing long lasting streaming connections, in which restarting of heimdall can lead to cascading errors.

Describe your idea

To make it more convenient, it would be helpful to let heimdall react on secret rotation for the Signer key material in addition to what has been implemented in #1230 and let it use new updated secrets.

Are there any workarounds or alternatives?

Restart heimdall

Version

v0.13.0-alpha

Additional Context

This FR has been discussed in https://discord.com/channels/1100447190796742698/1131484813258391665/1131484813258391665 and is related to #1036