docs: add CloudFront option for IRSA implementation without public S3 bucket

[omaraws]

Issue #, if available: None

Description of changes:
This PR adds documentation about using Amazon CloudFront as an alternative method to host OIDC discovery files and keys for IRSA implementation with EKS Anywhere. This solution is particularly useful for organizations that have policies restricting the use of public S3 buckets.

Testing (if applicable):
Verified the documentation renders correctly.

Documentation added/planned (if applicable):

• Added a note to the IRSA setup documentation in the "Create an OIDC provider" section
• Referenced the aws-samples/sample-eks-anywhere-irsa-cloudfront repository that demonstrates using CloudFront distributions to host OIDC files

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[eks-distro-bot]

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[eks-distro-bot]

Hi @omaraws. Thanks for your PR.

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