feat: auto-inject AWS account ID into telemetry from Lambda extension registration

[RaphaelManke]

Summary

Automatically extract the AWS account ID from the Lambda Extensions API registration response and inject it as the cloud.account.id attribute into all telemetry (traces, logs, metrics) via a confmap converter.

This implementation uses the OpenTelemetry Collector's converter pattern to mutate the loaded configuration, ensuring the account ID is automatically available without requiring configuration or environment variables.

Changes

• extensionapi/client.go: Added AccountId field to RegisterResponse and request the accountId feature via Lambda-Extension-Accept-Feature header
• accountidprocessor/converter.go: New confmap converter that automatically injects a resource processor for cloud.account.id attribute into all pipelines
• accountidprocessor/converter_test.go: Comprehensive tests for converter behavior (empty account ID, no pipelines, multiple pipelines, leading zeros)
• extensionapi/client_test.go: Tests for JSON unmarshaling with leading zero preservation
• lambdacomponents/default.go: Updated to accept accountID and return converter factories
• collector.go: Updated to accept and register custom converters
• manager.go: Updated to pass account ID through the initialization flow

Benefits

• Account ID automatically available in all telemetry without configuration
• No environment variables needed, uses AWS Lambda API response
• Follows OpenTelemetry Collector patterns
• Static injection at startup with no runtime overhead
• Comprehensive test coverage for edge cases (leading zeros, multiple pipelines)