This updates our Review Board Docker to sit on a more modern foundation

and to support ARM64 architectures.
We now use Ubuntu 22.04 LTS (upgrading from 20.04 LTS) and Python 3.11

(upgrading from 3.8).
The build script now uses docker buildx, which gives us

multi-architecture build support. We instruct it to build both amd64 and

arm64 images, giving consumers the option to install it in either

environment. This requires building either on an M1-based Mac or on a

Linux host with multi-arch emulation or cross-compilation enabled.
There is one important change to note: We do not build Perforce support

on arm64, as Perforce currently does not provide any arm64 builds

for Linux.

Successfully built and tested Docker images for both Intel and ARM

machines.