Support ARM64 based CPU

[amplitudesxd]

Describe the bug

As there isn't a build for ARM64 based CPUs, Postal cannot run on them and errors with "exec user process caused: exec format error".

To Reproduce

1. Use an ARM64-based server (Raspberry Pi, Hetzner Cloud ARM server, etc.)
2. Attempt to create a container with the Postal docker image
3. Observe error

Expected behaviour

I expect Postal to work on ARM, while ARM architecture wasn't used as much in servers previously, it's becoming increasingly popular with many dedicated/cloud server providers offering them.

Additional information/context

I've created a PR to add ARM builds in #2770.

[phillmorgan28]

@adamcooke Support appears to be broken
Error whilst pulling v3 images during postal initialize - no matching manifest for linux/arm64/v8 in the manifest list entries

[adamcooke]

This is intentional. Unfortunately it takes 20+ minutes to build for ARM. Until we can speed this up, ARM images are not built.

[willpower232]

We have had this problem too (building ARM images on GitHub), hopefully the ARM runners are available soon https://github.blog/changelog/2023-10-30-accelerate-your-ci-cd-with-arm-based-hosted-runners-in-github-actions/

[adamcooke]

We have a ARM server right here. We just need to set it up to run some self hosted runners.

[adamcooke]

Some progress is being made here. Specifically we can build the image on ARM and AMD64 in just over 2 minutes which is better than over 20.