Make block I/O stat Op parsing case insensitive

[danehlim]

Summary

Make logic that parses block I/O Op from docker stats case insensitive.

This is because docker stats could return values of Op which may or may not have consistent capitalization (for example, Docker returns values of Op such as "read" and "write" for cgroups v2 as opposed to "Read" and "Write" for cgroups v1). Thus, without the change in this pull request, ECS Agent currently is susceptible to potentially ignore data that it actually should take it into account for storage metrics that ECS surfaces to CloudWatch.

Implementation details

See "Summary" section above.

Testing

New tests cover the changes: yes (new unit test added and existing integ test updated)

Manually performed the following end to end test:

• Set up an ECS cluster with "Container Insights with enhanced observability" feature enabled with container instances using the latest AL2023 ECS-Optimized ARM64 AMI (which uses cgroups v2)
• In the cluster, launch an ECS task which explicitly writes to storage
• Observe that ECS emits a storage write metric value of 0 in CloudWatch
• Subsequently, stop ECS Agent and relaunch a custom ECS Agent incorporating the changes from this pull request
• After the custom ECS Agent has launched, confirm that ECS emits a nonzero storage write metric value in CloudWatch

Description for the changelog

Bugfix - Make block I/O stat Op parsing case insensitive

Additional Information

Does this PR include breaking model changes? If so, Have you added transformation functions?

No

Does this PR include the addition of new environment variables in the README?

No

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.