Add endpointslices permissions to the cloudwatch-agent-role

[sky333999]

Description of changes

Update cloudwatch-agent-role to add endpointslices permissions to match aws-observability/helm-charts#172.

License

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Requirements

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• If this commit includes changes to existing sample configurations, you acknowledge that you have confirmed this will not impact existing customer behavior.
• If not necessary, consider creating a new sample configuration for this change.