feat: build multiarch images

[matifali]

closes #185, closes #237

Important

The build and push script requires depot CLI to be set up and fail if run locally and the depot is unavailable. We can add a fallback method to use docker CLI in a follow-up PR (docker needs a bit more work to push multi-arch image manifest)

[matifali]

What is a safer way to test pushing? depot can push automatically, but here we are first scanning and then pushing manually.

[johnstcn]

What is a safer way to test pushing? depot can push automatically, but here we are first scanning and then pushing manually.

I think manually pushing is probably OK here; we can test one image/tag and if successful then push automatically.

[johnstcn]

I tested this out by performing the following steps on an arm64 machine (macOS):

• Editing out the line installing tonistiigi/binfmt in examples/lima/coder.yaml
• limactl start --name=coder ./examples/lima/coder.yaml
• Created basic Docker template
• Modified Docker template to reference image from depot.dev
• (Note: I had to manually pull the image inside the VM using the depot cli as I couldn't figure out how to pass basic auth creds for depot to the Docker daemon)

Result: workspace built successfully from template