feat: Hot reloading of TLS key stores

[dadrus]

Related issue(s)

closes #1227

Checklist

• I agree to follow this project's Code of Conduct.
• I have read, and I am following this repository's Contributing Guidelines.
• I have read the Security Policy.
• I have referenced an issue describing the bug/feature request.
• I have added tests that prove the correctness of my implementation.
• I have updated the documentation.

Description

This PR makes heimdall listening to changes in configured TLS key stores if secrets_reload_enabled is set to true. This way you can make use of a secret management service of your choice and rotate TLS keys/certificates used by heimdall while listening for incoming connections, as well as used when heimdall communicates to other systems via TLS mutual authentication (as of today only when communicating to Redis cache).

[codecov]

Codecov Report

Attention: Patch coverage is 91.89189% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 89.24%. Comparing base (2f9ba81) to head (9b3186d).
Report is 1 commits behind head on main.

Files	Patch %	Lines
internal/watcher/module.go	0.00%	5 Missing ⚠️
internal/watcher/noop_watcher.go	0.00%	2 Missing ⚠️
internal/watcher/watcher_impl.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1230      +/-   ##
==========================================
+ Coverage   89.21%   89.24%   +0.03%     
==========================================
  Files         266      269       +3     
  Lines        8771     8837      +66     
==========================================
+ Hits         7825     7887      +62     
- Misses        699      703       +4     
  Partials      247      247              

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