Add multi-arch images for development environments

[maggie44]

I notice that there isn't any multi arch images available, so for example you cannot pull balenalib/debian-python:3.8.6, but would instead need balenalib/amd64-debian-python:3.8.6.

Of course multi arch images wouldn't be much use for Balena device development right now, but when creating development environments we use the Balena images on our local systems to replicate the production environment as best as possible. Without multi-arch images, we have to ask developers to manually alter the Dockerfiles to reflect their systems. With MacBook M1 now requiring an ARM image, this problem is just going to get bigger.

It would be great to have multi-arch support, so that we could add balenalib/debian-python:3.8.6 into our development dockefiles and then have Docker identify which arch to pull.