fix: add error handling for insecure HTTP endpoints with TLS client configuration

[sandy2008]

Summary

This PR moves the insecure + TLS config validation into the core OTLP HTTP exporters in opentelemetry-go (trace, metric, and log), instead of relying on validation in external/config-wrapper code.

This aligns with feedback from open-telemetry/opentelemetry-go-contrib PR open-telemetry/opentelemetry-go-contrib#8560: these packages are maintained/released together, so the check should be enforced in this repo as well.

What changed

• Added exporter-level validation error:
  • "insecure HTTP endpoint cannot use TLS client configuration"
• Enforced in:
  • otlpmetrichttp client construction
  • otlploghttp client construction
  • otlptracehttp client startup (Start, since NewClient does not return an error)
• Added tests in all three exporters to cover:
  • Error when WithInsecure() and WithTLSClientConfig(...) are both set
  • No error when a custom WithHTTPClient(...) is provided (preserves existing precedence semantics)

Behavior

• Invalid config (insecure + TLS config) now fails fast directly in exporters.
• Existing WithHTTPClient override behavior remains unchanged.

Testing

Ran:

• go test ./... in exporters/otlp/otlpmetric/otlpmetrichttp
• go test ./... in exporters/otlp/otlplog/otlploghttp
• go test ./... in exporters/otlp/otlptrace/otlptracehttp

Related

• open-telemetry/opentelemetry-go-contrib PR (otelconf: fail closed when OTLP HTTP exporter uses http endpoint with TLS/mTLS config opentelemetry-go-contrib#8560)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.7%. Comparing base (76e6eec) to head (3106348).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7914   +/-   ##
=====================================
  Coverage   81.7%   81.7%           
=====================================
  Files        304     304           
  Lines      23333   23339    +6     
=====================================
+ Hits       19078   19086    +8     
+ Misses      3866    3864    -2     
  Partials     389     389           

Files with missing lines	Coverage Δ
exporters/otlp/otlplog/otlploghttp/client.go	83.5% <100.0%> (+0.2%)	⬆️
exporters/otlp/otlpmetric/otlpmetrichttp/client.go	81.0% <100.0%> (+0.2%)	⬆️
exporters/otlp/otlptrace/otlptracehttp/client.go	77.1% <100.0%> (+0.2%)	⬆️

... and 1 file with indirect coverage changes

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[dmathieu]

This will need changelog entries.

[sandy2008]

This will need changelog entries.

@dmathieu Done, added ;)

[sandy2008]

@pellared @dmathieu Thank you for approving it :) Do you know when can we get it merged :)?