Add documentation comparing EKS-A and Outpost

**What would you like to be added**:
In the EKS-A user documentation, describe how EKS-A is different from Outpost. The existing [Compare EKS Anywhere and EKS](https://anywhere.eks.amazonaws.com/docs/concepts/eksafeatures/) section is the suggested place to add this information. This could also point to existing [Deployment options](https://docs.aws.amazon.com/eks/latest/userguide/eks-deployment-options.html) in the AWS EKS docs:

**Why is this needed**:
There have been questions about how EKS-A is different from other AWS on-premises solutions, such as Outpost.

Start with the linked EKS Anywhere documentation's “Compare EKS Anywhere and EKS” section and review the linked AWS EKS Deployment options page. Add a clear comparison explaining how EKS-A differs from Outposts, with the AWS documentation link where useful. Done means the EKS-A docs answer the reported questions about these on-premises options.

Written by the indexing model from the issue text.