MacOS Selenium ARM Images

[andrewnicols]

The standard Selenium images do not currently run on MacOS with ARM chipsets.

Someone else has [with SeleniumHQ's blessing(https://github.com/SeleniumHQ/docker-selenium#experimental-mult-arch-aarch64armhfamd64-images) created a fork for ARM:

https://hub.docker.com/u/seleniarm

We should look into updating moodle-docker to run the seleniarm images on ARM architectures.

[skodak]

workaround is to use following in local.yml:

version: '2.4'
services:
  selenium:
    image: "seleniarm/standalone-chromium:latest"

I did not find any significant problems with it yet.

[rezaies]

version is obsolete