Migrate from API Key to Auth Token for sample tests

The LocalStack API key (LOCALSTACK_API_KEY) has been sunset and will no longer work for authentication. To ensure that the sample tests in this repository continue to execute successfully, migrate all usages of LOCALSTACK_API_KEY to the new LOCALSTACK_AUTH_TOKEN environment variable.

Tasks:

• Identify all places where LOCALSTACK_API_KEY is referenced and replace with LOCALSTACK_AUTH_TOKEN (mainly in makefile.yml)
• Update documentation and code comments where necessary
• Validate that sample tests pass with the new auth token

Impact:

Without this migration, sample tests will fail due to authentication errors since the API key mechanism is deprecated.