otellambda: allow custom attributes

[matbrito]

This PR introduces a new feature to the AWS Lambda OpenTelemetry Go instrumentation, allowing users to attach custom attributes to spans based on the Lambda event payload. This enhancement provides greater flexibility for enriching traces with application-specific context.

Changes

New Option: WithTraceAttributeFn

• Added a new option function, WithTraceAttributeFn, which accepts an TraceAttributeFn (a function that can extracts attributes from the event JSON).
• Updated the internal config struct to include a TraceAttributeFn field.
• The default extractor is a no-op, returning no attributes.

Instrumentation Logic Update

• During span creation, the configured TraceAttributeFn is called with the event payload.
• Any attributes returned by this function are appended to the span’s attributes.

Unit Tests

• Added a new test, TestWrapHandlerTracingWithTraceAttributeFn, to verify that custom attributes extracted from the event are correctly attached to the span.
• The test uses a mock and asserts that the expected custom attribute is present in the span.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: matbrito / name: Matheus Brito (c38eb7f, 97189ef, 0a52f98, 1d00cec, f6204d6, c09e34b, c006e68, 710de6b, e381002, 327cd75, 43c0d10, e99cd16)
• ✅ login: dmathieu / name: Damien Mathieu (60298d9, 5216c8d)

[matbrito]

#7557

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.7%. Comparing base (2e2c53f) to head (5216c8d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7556   +/-   ##
=====================================
  Coverage   78.7%   78.7%           
=====================================
  Files        186     186           
  Lines      14807   14816    +9     
=====================================
+ Hits       11656   11665    +9     
  Misses      2803    2803           
  Partials     348     348           

Files with missing lines	Coverage Δ
.../github.com/aws/aws-lambda-go/otellambda/config.go	100.0% <100.0%> (ø)
.../github.com/aws/aws-lambda-go/otellambda/lambda.go	89.6% <100.0%> (+0.5%)	⬆️

🚀 New features to boost your workflow:

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

[MrAlias]

Thanks for your interest in the project. Please provide a complete enhancement issue in #7557 prior to proposing a change here. Design and motivation can be discussed there.

[dmathieu]

@akats7 what do you think of this, as code owner?

[akats7]

This is a good update, definitely seems valuable