feat(appender-tracing): add experimental span attributes enrichment

[leghadjeu-christian]

Fixes #3221 Design discussion issue (if applicable) #

Changes

Add experimental experimental_span_attributes feature to enrich log records with attributes from active tracing spans. When enabled, span attributes are automatically included in log records. Event attributes take precedence on conflicts.

Merge requirement checklist

• [x] CONTRIBUTING guidelines followed
• [x] Unit tests added/updated (if applicable)
• [x] Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• [ ] Changes in public API reviewed (if applicable)