Shipping with Apple Silicon

Is there any place in the vars or config to specify a specific docker image platform?

Using Apple silicon chips to build the image creates an incompatibility issue when shipping to AWS ECS.

I had to manually create the image using:
`UFO_DOCKER_BUILD_OPTIONS="--platform=linux/amd64" UFO_ENV=env ufo docker build --push`

then manually ship it:
`UFO_ENV=env ufo ship --no-docker`
but I also had to tweak the config files in order to specify the correct image and for some reason this last command did not create a load balancer, so I had to add `config.elb.enabled = true`.

So in short, I found several issues when running the commands like that.

Is there a way to specify the platform (`--platform=linux/amd64`) when shipping using the standard `ufo ship` command?

Start by reproducing the standard `ufo ship` flow on Apple Silicon and compare it with the documented `ufo docker build --push` and `ufo ship --no-docker` commands. Trace the vars or config used for Docker platform selection and ECS shipping, then verify that a standard ship accepts `--platform=linux/amd64` and preserves the expected image and load-balancer configuration.

Written by the indexing model from the issue text.