Add CloudWatch Logs Subscription Filter Support for CloudTrail

Summary

This PR adds support for processing CloudTrail logs delivered via CloudWatch Logs subscription filters to the awslogsencodingextension. Previously, the extension only supported CloudTrail logs stored in S3.

Changes

Core Implementation

• New fromCloudWatch() method: Handles CloudTrail logs from CloudWatch Logs subscription filter format
• Format detection: Uses extractFirstKey() to detect the CloudWatch envelope ("messageType") vs S3 format ("Records")
• CloudWatch event parsing: Unmarshals individual CloudTrail events from logEvents[].message field (each message contains a single CloudTrail event as an escaped JSON string)
• Resource attributes: Sets CloudWatch-specific attributes (aws.log.group.names, aws.log.stream.names) in addition to CloudTrail attributes (cloud.provider, cloud.region, cloud.account.id)

Format Differences

S3 Format

{
  "Records": [
    { "eventVersion": "1.11", "eventName": "PutObject", ... },
    { "eventVersion": "1.11", "eventName": "GetObject", ... }
  ]
}

CloudWatch Format

{
  "messageType": "DATA_MESSAGE",
  "logGroup": "/aws/cloudtrail/logs",
  "logStream": "123456789010_CloudTrail_us-east-1",
  "logEvents": [
    {
      "id": "eventId1",
      "timestamp": 1418530010000,
      "message": "{\"eventVersion\":\"1.11\",\"eventName\":\"PutObject\",...}"
    },
    {
      "id": "eventId2",
      "timestamp": 1418530020000,
      "message": "{\"eventVersion\":\"1.11\",\"eventName\":\"GetObject\",...}"
    }
  ]
}

Key difference: In CloudWatch format, each logEvents[].message is an escaped JSON string containing a single CloudTrail event, whereas S3 files contain an array of events.

Configuration Example

receivers:
  awslambda:
    cloudwatch:
      encoding: awslogs_encoding

extensions:
  awslogs_encoding:
    format: cloudtrail

service:
  extensions: [awslogs_encoding]
  pipelines:
    logs:
      receivers: [awslambda]
      exporters: [otlp]

Related Issues

• Closes [awslogsencodingextension] Allow CloudTrail logs unmarshaling support for logs received through CloudWatch #45354

Testing

New Test Cases

• Valid CloudWatch subscription filter format: Tests the new CloudWatch format parsing with real CloudWatch subscription filter event structure
  • Input: testdata/cloudtrail_log_cw.json - CloudWatch subscription filter message with CloudTrail events
  • Expected output: testdata/cloudtrail_log_cw_expected.yaml - Properly mapped OpenTelemetry logs

Breaking Changes

None. This is a backwards-compatible addition that extends existing functionality.