Disable Rust dependencies while building cryptography for Docker

[gabriel-milan]

Summary

Fixes ARM builds for Docker (using one of two available approaches, see details below) (related to #1579 and #1606).

Solve the issue: #1579

Changelog

• Removes Rust dependencies for Python's cryptography package while building Docker image.

What's new?

Due to cryptography's recent dependencies on Rust (pyca/cryptography#5771), Raspberry Pi's arm/v7 platform (among others) became unsupported. In order to fix that, there are currently two available approaches:

• Disable Rust while building cryptography with the environment variable CRYPTOGRAPHY_DONT_BUILD_RUST=1 (chosen in this case)
  • Keeps cryptography up to date
  • I couldn't really find the downsides of disabling Rust
• Use an older version of cryptography (2.6.1 works fine for me in other projects)
  • Cryptography is outdated, can lead to security issues

You can see that when I've tried to build it using the Dockerfile I've customized it seems that the build has gone OK but, unfortunately, there's this issue:

Error: buildx call failed with: error: failed to solve: rpc error: code = Unknown desc = docker exporter does not currently support exporting manifest lists

Fortunately, this isn't related to the Docker image itself, but this: docker/buildx#59.

The purpose of this PR is to find out if this change to the Dockerfile is acceptable. If so, I can implement what is missing.

[Herklos]

Thanks @gabriel-milan good job ! 👍

[GuillaumeDSM]

I included your commit here #1612 to apply it on an updated branch, thanks a lot @gabriel-milan !

[gabriel-milan]

Thank you guys, can't wait to get this up and running on my RPi.

[GuillaumeDSM]

merged via #1612
we will soon have OctoBot back on armv7 🎉