docs: update docs for multi metrics provider support, fix API reference generator

[mowies]

This PR

• adjusts the API reference generator script to work with the metrics API under the metrics operator
• re-generates all metrics API references pages
• adjusts all KeptnMetricProvider occurrences to the new API version while also introducing the new type field
• adds some info about support for multiple providers of the same type

Part of #1144

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[codecov]

Codecov Report

Merging #1251 (6645050) into main (3c465d0) will decrease coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1251      +/-   ##
==========================================
- Coverage   59.30%   59.27%   -0.03%     
==========================================
  Files         133      133              
  Lines       10105    10105              
==========================================
- Hits         5993     5990       -3     
- Misses       3895     3897       +2     
- Partials      217      218       +1     

see 3 files with indirect coverage changes

Flag	Coverage Δ
certificate-operator	64.15% <ø> (ø)
component-tests	59.71% <ø> (-0.22%)	⬇️
lifecycle-operator	78.26% <ø> (ø)
metrics-operator	79.03% <ø> (ø)
scheduler	21.75% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[mowies]

FYI: @StackScribe the changes here will also be important for the upcoming YAML reference page for the KeptnMetricsProvider

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[StackScribe]

Note that I am about to submit a PR that deletes the concepts/metrics/_index.md file and moves that information to different files in the new structure. My PR will include the updates made in this PR.