Fix or remove ECS-ECR container app tutorial

[joe4dev]

The ECS-ECR container app tutorial is broken and has many issues: https://docs.localstack.cloud/tutorials/ecs-ecr-container-app/

We should either fix or remove it.

Motivation

• Initially reported by a pro customer
• Previously discussed in a prior update (May 2023) to this app: https://github.com/localstack/docs/pull/628#discussion_r1199253326
  • The LocalStack issue has been fixed in https://github.com/localstack/localstack/pull/8970
  • The app didn't work for me back in May 2023
• I retested (2023-10-17) and the tutorial and it still doesn't work for me.
  • The CloudFormation stack fails to deploy with a validation error An error occurred (ValidationError) when calling the CreateTargetGroup operation: A VPC ID must be specified

Further suggestions for improvement

• Use concrete naming suggestions instead of placeholders that need to be changed for no reason
• Avoid using naming collisions for <STACK_NAME> being used twice in different context
• Copy/pasting long blobs of partial files and then making them fit together is very cumbersome
• Consider providing a minimal example or use a repository to bootstrap the tutorial. The CloudFormation template is unnecessarily complex for the intended demonstration purpose