[Fargate] [EIP support]: add Elastic IP support for Fargate

**Tell us about your request**
New feature to allow EIP to be added to containers created with Fargate

**Which service(s) is this request for?**
Fargate

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
We're deploying a single container for a webapp into ECS with Fargate, and we don't need a ALB because the app is simple. We are trying to avoid a new IP for the container every time we deploy via Cloudformation, because it'd make the approach not sustainable.

**Are you currently working around this issue?**
ALB, but it's money we don't want to spend, so we have to take a decision here.

**Additional context**
no

**Attachments**
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