refactor!: Metrics service configuration changed

[dadrus]

Related issue(s)

None

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 the metrics service configuration more sound and also more secure.

Old configuration:

metrics:
  prometheus:
    host: "" # listens to all interfaces by default
    port: 10250
    metrics_path: /metrics

New configuration:

metrics: # no indirection, as above. all properties are on the top level
  enabled: true # can now be disabled. Defaults to `true`
  host: 127.0.0.1 # listens on loopback interface only
  port: 10250
  metrics_path: /metrics

The Helm chart has been updated as well and takes into account, that listening on loopback interface only will not allow metrics exposure. So the chart sets this value to 0.0.0.0. As in the past it does not configure a kubernetes service for this port. The chart has also been extended to support enabling and disabling of this service.

[codecov]

Codecov Report

Merging #452 (05b96b1) into main (8c891bf) will decrease coverage by 0.06%.
The diff coverage is 76.66%.

@@            Coverage Diff             @@
##             main     #452      +/-   ##
==========================================
- Coverage   87.91%   87.85%   -0.06%     
==========================================
  Files         202      200       -2     
  Lines        8077     8088      +11     
==========================================
+ Hits         7101     7106       +5     
- Misses        804      809       +5     
- Partials      172      173       +1     

Impacted Files	Coverage Δ
internal/config/metrics.go	0.00% <0.00%> (ø)
internal/handler/metrics/module.go	50.00% <56.66%> (+31.25%)	⬆️
internal/handler/decision/app.go	79.59% <100.00%> (+1.33%)	⬆️
internal/handler/management/app.go	75.60% <100.00%> (+1.92%)	⬆️
internal/handler/profiling/module.go	24.00% <100.00%> (+6.60%)	⬆️
internal/handler/proxy/app.go	80.00% <100.00%> (+1.27%)	⬆️
internal/prometheus/module.go	100.00% <100.00%> (ø)
internal/fiber/middleware/prometheus/defaults.go	0.00% <0.00%> (-100.00%)	⬇️

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