Support YAML only configuration

[jefchien]

Description of the issue

The CloudWatch agent added support for supplemental OTEL Collector YAML configurations as part of #1371 that could be merged with pre-existing agent JSON configurations. It still required a JSON for the agent to run.

Description of changes

Removes the JSON requirement (#2029). This allows the CloudWatch agent to be run with just OTEL Collector YAMLs.

sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a fetch-config -c file:/tmp/config.yaml -s

Corresponding agenthealth improvements: #2039, #2059

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

https://github.com/aws/amazon-cloudwatch-agent/actions/runs/23500580900

Requirements

Before commiting your code, please do the following steps.

1. Run make fmt and make fmt-sh
2. Run make lint

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Integration Tests

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[mitali-salvi]

Closing in favor of #2062