[Metrics] Exclude list for tags on Metrics

[nabutabu]

Fixes #4427
Design discussion issue open-telemetry/opentelemetry-specification#4188

Changes

Adds an exclude list to MetricStreamConfiguration and FindMetricAggregatorsExcludeTag method that returns the correct list for the current view

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 89.28571% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.21%. Comparing base (68bdfce) to head (b7893ac).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/OpenTelemetry/Metrics/ThreadStaticStorage.cs	79.16%	5 Missing ⚠️
src/OpenTelemetry/Metrics/AggregatorStore.cs	83.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7373      +/-   ##
==========================================
- Coverage   90.33%   90.21%   -0.13%     
==========================================
  Files         289      289              
  Lines       15745    15820      +75     
==========================================
+ Hits        14224    14272      +48     
- Misses       1521     1548      +27     

Flag	Coverage Δ
unittests-Project-Experimental	90.21% <89.28%> (-0.11%)	⬇️
unittests-Project-Stable	90.13% <89.28%> (-0.22%)	⬇️

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

Files with missing lines	Coverage Δ
src/OpenTelemetry/Metrics/Exemplar/Exemplar.cs	85.96% <100.00%> (+0.25%)	⬆️
...try/Metrics/Exemplar/FixedSizeExemplarReservoir.cs	93.33% <100.00%> (+0.74%)	⬆️
src/OpenTelemetry/Metrics/MeterProviderSdk.cs	94.30% <100.00%> (+0.16%)	⬆️
src/OpenTelemetry/Metrics/MetricStreamIdentity.cs	86.74% <100.00%> (+0.29%)	⬆️
...elemetry/Metrics/View/MetricStreamConfiguration.cs	100.00% <100.00%> (ø)
src/OpenTelemetry/ReadOnlyFilteredTagCollection.cs	100.00% <100.00%> (ø)
src/OpenTelemetry/Metrics/AggregatorStore.cs	89.63% <83.33%> (-0.47%)	⬇️
src/OpenTelemetry/Metrics/ThreadStaticStorage.cs	82.85% <79.16%> (-1.93%)	⬇️

... and 6 files with indirect coverage changes

[github-actions]

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[nabutabu]

Decisions that require review

TagKeys and ExcludedTagKeys combination behavior

State	Behavior	New in PR?
Both null	All tags preserved	No
TagKeys = []	All measurements collapse to zero-tag metric point	No
ExcludedTagKeys = []	All tags preserved (identical to default, but goes through exclude code path)	Yes
Both non-null (including both [])	Validate() throws, view is dropped with a logged warning (event ID 41), instrument falls back to default behavior	Yes

Order sensitivity in ExcludedTagKeys

ExcludedTagKeys uses element-wise comparison (same as TagKeys). ["a","b"] and ["b","a"] produce different MetricStreamIdentity values even though the filtering behavior is identical. This is a known limitation inherited from the pre-existing TagKeys behavior.