refactor: Refactor AppMesh-mTLS example.

[rodrigobersa]

What does this PR do?

Refactor example/appmesh-mtls.

Motivation

Terraform EKS Blueprints v5 release.

More

• Yes, I have tested the PR using my local account setup (Provide any test evidence report under Additional Notes)
• Yes, I have updated the docs for this feature
• Yes, I ran pre-commit run -a with this PR

For Moderators

• E2E Test successfully complete before merge?

Additional Notes

pre-commit run --files examples/appmesh-mtls/*
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check for merge conflicts................................................Passed
detect private key.......................................................Passed
detect aws credentials...................................................Passed
Terraform fmt............................................................Passed
Terraform docs...........................................................Passed
Terraform validate with tflint...........................................Passed
Terraform validate.......................................................Passed