docs(metrics/dashboard): Fix Metrics docs and enhance example dashboard with more metrics

[lukepatrick]

Updated metrics.md docs after reviewing alongside Datadog metrics - there is also a DD PR to update their docs/integrations here

This PR also updates the example grafana dashboard with more examples using more Argo CD metrics.

• AppSet Stats
• OCI Stats
• Kubectl Stats

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.62%. Comparing base (b543e18) to head (d814c1d).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #25772      +/-   ##
==========================================
- Coverage   62.63%   62.62%   -0.01%     
==========================================
  Files         353      353              
  Lines       50159    50159              
==========================================
- Hits        31416    31414       -2     
- Misses      15725    15727       +2     
  Partials     3018     3018              

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