Docker images: fix raspbian-bullseye, install python3-venv

[graebm]

Issue:
awslabs/aws-crt-python#573 needs python3's venv installed on all docker images, due to PEP 668.

While trying to update our raspbian-bullseye image, I discovered it's been broken for months. We'd been hacking around this by not even trying to build it anymore, copy/pasting an old working version instead.

Description of changes:

• Install python3-venv in Docker images that didn't already have it
• Fix raspbian-bullseye image.
  • The old image was getting 404 from some repository while running apt-get update
  • Use different base image: https://github.com/dtcooper/raspberrypi-os-docker. This was the only easily available bullseye image I could find. The implementation looks simple, and it's working.
  • Remove extra stuff from this docker image, like building additional versions of python. I don't know what these were used for (@xiazhvera do you know?). None of our other docker images go through this trouble to build extra python versions. This is already the slowest docker image, due to being armv7, so removing extra work and complication seems extra good.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[xiazhvera]

I don't remember why we added the various versions of Python. Probably it is for running different Python versions in CI, as we do run python3.7-3.12 for linux (and musl). However, the currently CI did not run against those Python version any more. I think we can remove them safely.