trace,metric,log: WithInstrumentationAttributes options to merge attributes

[pellared]

What

Fix WithInstrumentationAttributes options in go.opentelemetry.io/otel/trace, go.opentelemetry.io/otel/metric, and go.opentelemetry.io/otel/log to properly merge attributes when passed multiple times instead of replacing them. Attributes with duplicate keys will use the last value passed.

Why

Per #7287 (review) and #7287 (comment)

Not that this does not address #7217. This is left to a seperate PR to not scope creep this one. CC @axw

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.9%. Comparing base (63f1ee7) to head (17f2711).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7300   +/-   ##
=====================================
  Coverage   82.9%   82.9%           
=====================================
  Files        265     265           
  Lines      24898   24938   +40     
=====================================
+ Hits       20650   20688   +38     
- Misses      3873    3875    +2     
  Partials     375     375           

Files with missing lines	Coverage Δ
log/logger.go	100.0% <100.0%> (ø)
metric/config.go	100.0% <100.0%> (ø)
trace/config.go	96.8% <100.0%> (+0.4%)	⬆️

... and 1 file with indirect coverage changes

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[Copilot]

Pull Request Overview

This PR fixes the WithInstrumentationAttributes options across OpenTelemetry's trace, metric, and log packages to properly merge attributes when called multiple times instead of replacing them. When duplicate attribute keys are provided, the last value takes precedence.

• Implements attribute merging functionality using attribute.NewMergeIterator
• Updates documentation to clarify the merging behavior
• Adds comprehensive test coverage for various merging scenarios

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
trace/config.go	Adds mergeSets helper and updates WithInstrumentationAttributes to merge instead of replace
trace/config_test.go	Adds comprehensive tests for attribute merging behavior
metric/config.go	Updates WithInstrumentationAttributes to use merging logic (references shared mergeSets)
metric/config_test.go	Adds tests for metric attribute merging scenarios
log/logger.go	Adds mergeSets helper and updates WithInstrumentationAttributes for merging
log/logger_test.go	Adds tests for log attribute merging scenarios
CHANGELOG.md	Documents the fix in the unreleased section

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[MrAlias]

🥇

[flc1125]

👍