Make extension script allow for multiarch builds

[dgiebert]

Is your feature request related to a problem? Please describe. Currently, the extensions create a single container image for a build that has a specific architecture (amd64)

Describe the solution you'd like For the UI Extension that uses it e.g. https://github.com/kubewarden/ui

• Enable buildx: https://github.com/marketplace/actions/docker-setup-buildx#usage

In the dashboard enhance it to:

• Release a container image per architecture
• Create a manifest that bundles all specified architectures

[blackwood821]

I just ran into this issue as well:

e4194ad3a5bf:/var/lib/rancher # kubectl -n cattle-ui-plugin-system logs deploy/rancher-extension-triton
exec /usr/sbin/nginx: exec format error

The issue turned out to be that I ran yarn publish-pkgs -c ... on a Mac with an Apple chip which resulted in the docker image being built for arm64 but I needed it to be built for linux/amd64.

To work around the issue I manually added --platform linux/amd64 to ./node_modules/@rancher/shell/scripts/extension/helm/scripts/package in my project.