[Develop][Bug] Fix incorrect timestamp parsing for chef-client.log in CloudWatch Agent (#3068)

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

Author: hehe7318

CHANGELOG.md

@@ -31,6 +31,7 @@ This file is used to list changes made in each version of the AWS ParallelCluste
   - Open MPI: openmpi40-aws-4.1.7-2 and openmpi50-aws-5.0.8-11
 
 **BUG FIXES**
+- Fix incorrect timestamp parsing for chef-client.log in CloudWatch Agent configuration.
 - Prevent cluster readiness check failures due to instances launched while the check is in progress.
 - Fix race condition where compute nodes could deploy the wrong cluster config version after an update failure.
 

cookbooks/aws-parallelcluster-environment/files/cloudwatch/cloudwatch_agent_config.json

@@ -4,6 +4,7 @@
     "default": "%Y-%m-%d %H:%M:%S,%f",
     "bracket_default": "[%Y-%m-%d %H:%M:%S]",
     "slurm": "%Y-%m-%dT%H:%M:%S.%f",
+    "chef": "[%Y-%m-%dT%H:%M:%S",
     "json": ""
   },
   "log_configs": [
@@ -82,7 +83,7 @@
       "feature_conditions": []
     },
     {
-      "timestamp_format_key": "default",
+      "timestamp_format_key": "chef",
       "file_path": "/var/log/chef-client.log",
       "log_stream_name": "chef-client",
       "schedulers": [