Add onprem test back

[movence]

Test update PR: https://github.com/aws/amazon-cloudwatch-agent-test/pull/635

Description of the issue

OnPrem integ test had been removed due to broken validation

Description of changes

Add back Onprem test that validates logs on Ubuntu25 and Debian12. There is no reason to cover all supported non-AL OSes since it's simple set up with:

• Local creds file
• IMDS disabled

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/20178604561

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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