[EKS/Fargate] [request]: Support Fargate Spot for EKS

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**Tell us about your request**
Provide the option to select `FARGATE_SPOT` as the Fargate Provider when creating an EKS Fargate Profile, like in ECS.

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

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Cost optimization and lower administration overhead for interruption tolerant workloads on EKS.

**Are you currently working around this issue?**
Yes, by using EC2 Spot Fleets.

Start by reviewing the EKS Fargate Profile provider option and the ECS Fargate Spot behavior named in the request. Compare these with the EC2 Spot Fleet workaround and define what selecting FARGATE_SPOT should enable for interruption-tolerant workloads. Done means the requested provider is supported for EKS Fargate Profiles and its behavior is documented.

Written by the indexing model from the issue text.