[ECS] [APIGateway]: Allow APIGateway to directly route requests to ECS containers

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**Tell us about your request**
I would like for ECS to be able to directly handle requests from APIGateway

**Which service(s) is this request for?**
ECS (we use Fargate, but this particular request could be for any kind of ECS workload)

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
I want to specify a URL route in APIGateway and I want those routes to be sent directly to ECS containers without the need for an extra load balancer in the way.

**Are you currently working around this issue?**
We provisioned an ALB and are only using it to service requests. ALBs are great but they do not have the same kind of AuthN/AuthZ capabilities/integrations that APIGateway provides.

No repository files, tests, or entry points are named. Start by reviewing the APIGateway, ECS/Fargate, and ALB integration requirements described in the issue; done means APIGateway routes requests directly to ECS containers without an ALB while preserving its AuthN/AuthZ capabilities.

Written by the indexing model from the issue text.