Use api_gateway_stage for managing APIGW stages with Terraform instead of api_gateway_deployment stage_name

Attempting to enhance some of the features/functionality of Chalice with Terraform during our deploys, but we're limited because Chalice does not expose the API Gateway stage (ie. for associating a WAF ACL with APIGW stage)

The AWS provider for Terraform has been updated and also no longer recommends using `stage_name` in `api_gateway_deployment` to manage API Gateway stages as Chalice does today.

Start by tracing Chalice's Terraform generation for API Gateway deployments and the use of api_gateway_deployment stage_name. Verify how API Gateway stages are currently represented and how Terraform can associate a WAF ACL with one. Done means stages are managed through api_gateway_stage while preserving deploy behavior and exposing the stage for external configuration.

Written by the indexing model from the issue text.