[Develop][Bug] Fix incorrect timestamp parsing for chef-client.log in CloudWatch Agent

[hehe7318]

Description of changes

This is a cherry-pick PR of #3061

The CloudWatch Agent configuration was using the default timestamp format (%Y-%m-%d %H:%M:%S,%f) for chef-client.log, but Chef/Cinc outputs ISO 8601 timestamps in format: [YYYY-MM-DDTHH:MM:SS+TZ].

This mismatch caused CloudWatch to fail parsing timestamps, resulting in log lines being associated with incorrect timestamps.

• Add new 'chef' timestamp format: [%Y-%m-%dT%H:%M:%S
  (Note: CloudWatch Agent's %z only supports timezone without colon like -0700, but Chef outputs +02:00 format. We only match up to seconds and let CloudWatch handle the rest.)
• Update chef-client.log configuration to use the new 'chef' format

Tests

Manually tests done, I create a cluster and export the cluster logs. Now in the chef-client log, I can see CW timestamp matches chef timestamp, e.g.:

2025-12-12T20:14:16.000Z [2025-12-12T20:14:16+00:00] INFO: Retrying execution of execute[check if clustermgtd heartbeat is available], 29 attempts left
2025-12-12T20:15:38.000Z [2025-12-12T20:15:38+00:00] INFO: Waiting for static fleet capacity provisioning
2025-12-12T20:15:07.000Z [2025-12-12T20:15:07+00:00] INFO: Waiting for static fleet capacity provisioning

Reference

https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch-Agent-Configuration-File-Details.html#CloudWatch-Agent-Configuration-File-Logssection
Expand CloudWatch agent configuration file: Logs section section:

%z
Time zone, expressed as the offset between the local time zone and UTC. For example, -0700. Only this format is supported. For example, -07:00 isn't a valid format.

Checklist

• Make sure you are pointing to the right branch.
• If you're creating a patch for a branch other than develop add the branch name as prefix in the PR title (e.g. [release-3.6]).
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

Please review the guidelines for contributing and Pull Request Instructions.

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

[gmarciani]

Same comment as #3061 (comment)