Fix EKS cluster detection

[musa-asad]

Description of the issue

To detect whether the CloudWatch Agent is running on EKS, we look for a ConfigMap named aws-auth, which is only supported for EKS and maps IAM users/roles to K8s RBAC for API access. However, aws-auth is now deprecated and isn't created on new EKS clusters, which marks the CloudWatch Agent as running on native K8s, not EKS, which is not accurate.

A suggestion from an issue is to inspect the serviceaccount token and look for the issuer field (iss). It contains the unique OIDC url for the EKS cluster.

Relevant issue: #1249.

Description of changes

• Add logic to query API server for issuer field as a fall-back.
• Update unit tests to reflect changes.
  • resetTestState() forces re-evaluation of the IsEKS() singleton for each test.

License

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Tests

Before

After

For testing, added a debug line:

Requirements

Before commit the code, please do the following steps.

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