Explicitly tell to move away from the Fargate driver

What does this MR do?

This change updates the docs around the no-longer-maintained Fargate Driver for GitLab Runner. The modification expands a recommendation to clarify that when using Amazon EKS (a managed Kubernetes service), users may prefer the standard Kubernetes executor over the Fargate custom executor.

As it currently stands the docs seem to give the idea that you can use Fargate with an EKS Cluster to somehow workaround the limitation of not having an image per CI/CD job.

Related issues

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