exporters: support MAP attributes

[pellared]

Fixes #8163

Add end-to-end exporter handling for attribute.SLICE in the remaining paths that still treated it as invalid or relied on fallback formatting.

Changes:

• encode attribute.MAP as OTLP AnyValue_AnyValue_KvlistValue for trace, log, and metric transforms
• serialize Zipkin MAP attributes using the non-OTLP AnyValue string representation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.5%. Comparing base (e708781) to head (d6332d1).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #8453   +/-   ##
=====================================
  Coverage   83.4%   83.5%           
=====================================
  Files        322     322           
  Lines      25667   25692   +25     
=====================================
+ Hits       21431   21456   +25     
  Misses      3854    3854           
  Partials     382     382           

Files with missing lines	Coverage Δ
...otlp/otlplog/otlploggrpc/internal/transform/log.go	96.3% <100.0%> (+<0.1%)	⬆️
...otlp/otlplog/otlploghttp/internal/transform/log.go	96.3% <100.0%> (+<0.1%)	⬆️
...ric/otlpmetricgrpc/internal/transform/attribute.go	97.1% <100.0%> (+0.1%)	⬆️
...ric/otlpmetrichttp/internal/transform/attribute.go	97.1% <100.0%> (+0.1%)	⬆️
...tlp/otlptrace/internal/tracetransform/attribute.go	97.2% <100.0%> (+0.1%)	⬆️
exporters/zipkin/model.go	99.4% <100.0%> (ø)

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

This PR completes end-to-end support for the new attribute.MAP type across the remaining exporter transform paths, ensuring MAP attributes are encoded as OTLP AnyValue.KvlistValue (and rendered appropriately for Zipkin’s deprecated tag encoding). This aligns exporter behavior with the attribute.Value.String() AnyValue representation rules and resolves the linked MAP-handling gap.

Changes:

• Encode attribute.MAP as OTLP AnyValue_KvlistValue in trace/log/metric attribute transforms (including shared gotmpl templates and generated exporter code).
• Add comprehensive nested MAP test coverage (MAP containing bytes, slices, nested maps, and empty values) across the affected OTLP transform test suites.
• Extend Zipkin’s deprecated exporter to serialize MAP attributes using attribute.Value.String() and add a validating JSON test; document the user-visible change in CHANGELOG.md.

Reviewed changes

Copilot reviewed 9 out of 17 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/shared/otlp/otlpmetric/transform/attribute.go.tmpl	Add MAP → OTLP KvlistValue encoding in shared metric attribute transform template.
internal/shared/otlp/otlpmetric/transform/attribute_test.go.tmpl	Add MAP attribute golden expectations (including nested MAP/SLICE cases) to metric transform template tests.
internal/shared/otlp/otlplog/transform/log.go.tmpl	Add MAP → OTLP KvlistValue encoding in shared log attribute transform template.
internal/shared/otlp/otlplog/transform/attr_test.go.tmpl	Add MAP attribute golden expectations (including nested MAP/SLICE cases) to log transform template tests.
exporters/zipkin/model.go	Treat MAP like SLICE and serialize via non-OTLP AnyValue string representation (Value.String()).
exporters/zipkin/model_test.go	Add Zipkin MAP serialization test validated with assert.JSONEq.
exporters/otlp/otlptrace/internal/tracetransform/attribute.go	Add MAP → OTLP KvlistValue encoding for trace exporter attribute transform.
exporters/otlp/otlptrace/internal/tracetransform/attribute_test.go	Add trace attribute transform test coverage for MAP → KvlistValue (nested structures included).
exporters/otlp/otlpmetric/otlpmetrichttp/internal/transform/attribute.go	Add MAP → OTLP KvlistValue encoding for OTLP/HTTP metric exporter transform.
exporters/otlp/otlpmetric/otlpmetrichttp/internal/transform/attribute_test.go	Add MAP transform expectations for OTLP/HTTP metric exporter tests.
exporters/otlp/otlpmetric/otlpmetricgrpc/internal/transform/attribute.go	Add MAP → OTLP KvlistValue encoding for OTLP/gRPC metric exporter transform.
exporters/otlp/otlpmetric/otlpmetricgrpc/internal/transform/attribute_test.go	Add MAP transform expectations for OTLP/gRPC metric exporter tests.
exporters/otlp/otlplog/otlploghttp/internal/transform/log.go	Add MAP → OTLP KvlistValue encoding for OTLP/HTTP log exporter transform.
exporters/otlp/otlplog/otlploghttp/internal/transform/attr_test.go	Add MAP transform expectations for OTLP/HTTP log exporter tests.
exporters/otlp/otlplog/otlploggrpc/internal/transform/log.go	Add MAP → OTLP KvlistValue encoding for OTLP/gRPC log exporter transform.
exporters/otlp/otlplog/otlploggrpc/internal/transform/attr_test.go	Add MAP transform expectations for OTLP/gRPC log exporter tests.
CHANGELOG.md	Record exporter MAP support as a user-visible addition.

Files not reviewed (8)

• exporters/otlp/otlplog/otlploggrpc/internal/transform/attr_test.go: Generated file
• exporters/otlp/otlplog/otlploggrpc/internal/transform/log.go: Generated file
• exporters/otlp/otlplog/otlploghttp/internal/transform/attr_test.go: Generated file
• exporters/otlp/otlplog/otlploghttp/internal/transform/log.go: Generated file
• exporters/otlp/otlpmetric/otlpmetricgrpc/internal/transform/attribute.go: Generated file
• exporters/otlp/otlpmetric/otlpmetricgrpc/internal/transform/attribute_test.go: Generated file
• exporters/otlp/otlpmetric/otlpmetrichttp/internal/transform/attribute.go: Generated file
• exporters/otlp/otlpmetric/otlpmetrichttp/internal/transform/attribute_test.go: Generated file