Document Docker build for cross platform images (e.g build on macOS and deploy to amd64)

At Anomaly we primarily use `macOS` for development and as Apple moves to Apple Silicon the development environments are moving to `arm` based CPUs, but most of our deployments are still under `amd64` (Intel or AMD based CPUs).

This has caused issues in the past, this should be documented properly and possibly even be made into a `Task` endpoint

```
docker build --platform=linux/amd64 -t "anomalyhq/accacia-server:0.2.0" -f Dockerfile .
```