Update appmesh-gateway in demo

[cdenneen]

Currently the demo for Progressive Delivery from:

https://eks.handson.flagger.dev/profile/#install-app-mesh

and

https://weaveworks-gitops.awsworkshop.io/50_workshop_5_accelerating_sdlc/30_install_appmesh/01_install_app_mesh.html

point to the demo branch of this repo.

the demo/ingress/appmesh-gateway.yaml however needs to be modified to stop using a deprecated Chart that is no longer supported and use the official eks-chart.

The chart change however creates some additional work because the old chart required mesh.name parameter and the new one does not have anything equivalent.

[cdenneen]

If it wasn't for: https://github.com/weaveworks/eks-appmesh-profile/blob/demo/demo/ingress/appmesh-gateway.yaml.tmpl#L14 I would submit the PR to change repo to https://aws.github.io/eks-charts and version to 0.1.4 but since I don't know what to do with this parameter for mesh.name I didn't open a PR at this time.