[EKS][Fargate]: prevent Fargate Profiles with duplicate Selectors from being Created

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**Tell us about your request**

I would like to request validation that prevents EKS Fargate profiles with the *exact* same selectors from being created.

**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?**

Having this problem unsolved creates circumstances with unpredictable behavior where pods can be scheduled when "selected" by one profile and where pods can fail to start when selected by another profile.

**Are you currently working around this issue?**

We identified the problem when we identified two Fargate profiles with the same selectors in which *one* profile had a properly configured IAM Role whereas another profile did *not* have a properly configured IAM Role.

**Additional context**

This situation can be duplicated by running the CloudFormation file below and removing one of the IAM Profiles from a Fargate Profile. The current solution is to avoid the situation (i.e. avoid human error) or to manually resolve if the situation occurs. _As I write this, I realize the other option might be to provide or present a misconfiguration notice if a Fargate Profile is improperly configured.

**Attachments**

[eks_in_fargate_dup.yaml.txt](https://github.com/aws/containers-roadmap/files/6928453/eks_in_fargate_dup.yaml.txt)

Start by reproducing the duplicate-selector case using the attached eks_in_fargate_dup.yaml.txt CloudFormation file, including the differing IAM role configuration described in the issue. Determine where EKS Fargate profile creation could validate exact duplicate selectors and define what prevention or misconfiguration notice should look like.

Written by the indexing model from the issue text.