feat: Add more metrics signal in fake data generator

[ThomsonTan]

Change Summary

Updates the static metrics signal generator from a minimal 2-type (Sum/Gauge) alternation with fixed attributes to a realistic multi-type signal covering all five OTLP metric kinds, with configurable attributes and data points per metric.

What issue does this PR close?

• Closes #NNN

How are these changes tested?

The changes are tested via 5 new unit tests

Are there any user-facing changes?

[codecov]

Codecov Report

❌ Patch coverage is 99.00332% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.06%. Comparing base (9f8e589) to head (0337868).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2566    +/-   ##
========================================
  Coverage   88.06%   88.06%            
========================================
  Files         631      631            
  Lines      233175   233445   +270     
========================================
+ Hits       205349   205591   +242     
- Misses      27302    27330    +28     
  Partials      524      524            

Components	Coverage Δ
otap-dataflow	89.77% <99.00%> (-0.01%)	⬇️
query_abstraction	80.61% <ø> (ø)
query_engine	90.74% <ø> (ø)
otel-arrow-go	52.45% <ø> (ø)
quiver	92.27% <ø> (ø)

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[lalitb]

This looks good for making the static metrics generator much more useful than the previous minimal implementation. One high-level suggestion as subsequent PR - consider making the metric generation more invariant-driven, where one underlying synthetic distribution is chosen first and the related fields are derived from it. That would reduce the chance of internal inconsistencies (as we see now) and make the generated metrics feel more realistic.