fix(docker): use dynamic architecture grain instead of hardcoded amd64

[jonathanlooi]

Problem

The Docker apt sources file has Architectures: amd64 hardcoded, which causes SIFT
installation to fail silently on ARM64 systems — the repository is configured for the
wrong architecture so docker-ce cannot be found.

Fix

Replace the hardcoded value with a Jinja grain lookup:
Architectures: {{ grains['osarch'] | replace('aarch64', 'arm64') }}
This writes the correct architecture (amd64 or arm64) at install time.

Tested on

• Ubuntu 22.04 LTS ARM64 running in UTM on Apple Silicon (M-series Mac)

[jonathanlooi]

I published this small repo describing some more details about how I got it running on my m3 mac https://github.com/jonathanlooi/sift-on-arm