Add integration test for journald

[Paamicky]

Description of the issue

Adds integration tests for the journald log collection feature. Tests validate that the journald pipeline correctly collects, filters, and delivers logs to CloudWatch.

Description of changes

• Feature test (test/feature/linux/journald_logs/) - Consolidated test file with 4 test functions validating units, priority, matches, and regex filtering. Uses a single EC2 instance with all 4 collect_list entries. Validates that only matching entries appear in each CloudWatch log stream.
  • Log state test (test/log_state/journald/) — Tests cursor persistence across agent restarts to validate no missing logs
  • Basic validator — Added journald-specific fields (LogUnit, LogPriority, LogIdentifier) to LogValidation model. Updated ValidateLogs Journald case to validate unit, priority, and identifier fields.
  • Test case generator — Registered journald tests in ec2_linux and ec2_selinux sections with AL2/AL2023 targets.

License

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Tests

All Journald tests passes: https://github.com/aws/amazon-cloudwatch-agent/actions/runs/25865272301

[TravisStark]

should these be deleted?