build: fix devcontainer for arm64 machines
The devcontainer image is only built for amd64 architecture. This makes it incompatible with arm64 machines like Apple silicon macs. Adding the --platform=linux/amd64 makes this run on Apple silicon Macs.
This has been tested with Podman on an M1 Max Macbook pro
Also moved the other settings under the more appropriate customizations
key as per the devcontainers spec as defined in https://containers.dev/supporting