feat: Add validation on argocd_applications app name

[catmand00]

‼️ PLEASE READ THIS FIRST ‼️

The direction for EKS Blueprints will soon shift from providing an all-encompassing, monolithic "framework" and instead focus more on how users can organize a set of modular components to create the desired solution on Amazon EKS. We have updated the examples to show how we use the https://github.com/terraform-aws-modules/terraform-aws-eks for EKS cluster and node group creation. We will not be accepting any PRs that apply to EKS cluster or node group creation process. Any such PR may be closed by the maintainers.

We are hitting also the pause button on new add-on creations at this time until a future roadmap for add-ons is finalized. Please do not submit new add-on PRs. Any such PR may be closed by the maintainers.

Please track progress, learn what's new and how the migration path would look like to upgrade your current Terraform deployments. We welcome the EKS Blueprints community to continue the discussion in issue #1421

What does this PR do?

Add validation to the var.applications variable used by argocd submodule, which uses the var.argocd_applications variable from the root module. The allowed name of the key is restricted by the same restrictions on kubernetes pod names, since the key is used for the name for the Application object, and the Application uses its name as the prefix of the resulting pod.
🛑 Please open an issue first to discuss any significant work and flesh out details/direction - we would hate for your time to be wasted.
Consult the CONTRIBUTING guide for submitting pull-requests.

Motivation

• Resolves Suggestion: validate the argocd_application keys early terraform-aws-eks-blueprints-addons#87

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

I have tested this locally using the same config that resulted in an error (linked in the related Issue), and I receive the error during the plan phase instead (as intended). Changing the name to test-app passes the validation (also intended).

[bryantbiggs]

Thank you!

[bryantbiggs]

@catmand00 would you mind opening the same PR in our new addons repo https://github.com/aws-ia/terraform-aws-eks-blueprints-addons when you get a chance - thank you!