Rename Graviton section to "Taints and Tolerations"

### What would you like to be added?

The section in Fundamentals -> Managed Node Groups -> Graviton Instances should be renamed to reflect that it is really an lab on Taints and Tolerations. The fact that it is using Graviton is just an example, and the same technique could be used for other purpose e.g. GPU instances.

Secifically referring to: https://github.com/aws-samples/eks-workshop-v2/blob/main/website/docs/fundamentals/managed-node-groups/graviton/index.md

### Why is this needed?

This is first and foremost an EKS workshop , so the audience interest is in Kubernetes and how to run Kubernetes on AWS. The general concept that the audience wants to learn is how they can use taints and tolerations with managed node groups, not Graviton specifically. So the current title is not helpful.

Start with website/docs/fundamentals/managed-node-groups/graviton/index.md and inspect the section heading and any nearby wording that refers specifically to Graviton. Rename the section to reflect Taints and Tolerations while preserving the lab content, then verify that the rendered workshop navigation and links still work.

Written by the indexing model from the issue text.