Multi-arch Build from Multiple Dockerfiles

[gemblerz]

User ML plugins are based mostly on our base image: CUDA10.2-L4T and CUDA11.0-amd64. We will need to support multiple Dockerfile for the plugins to be built on multi-arch.

User's Dockerfile will have more than one to build the plugin for l4t and amd64,

# Dockerfile.l4t
FROM waggle/plugin-base:1.1.1-ml-cuda10.2-l4t
...

# Dockerfile.amd64
FROM waggle/plugin-base:1.1.1-ml-cuda11.0-amd64
...

Docker buildx imagetools is useful command to create an image from source images. We need to enable this feature in our ECR and have users submit more than one Dockerfile (if needed) to build multi-arch image for the plugin.