Fixes #4425 so tests work after Docker setup

[jimmyli97]

Resolves #4425

Description

Fixes the Docker setup files so that tests pass out of the box, by installing latest version of Chrome and also setting the DOCKER environment variable.

Tests use Cuprite which relies on a headless Chrome browser. However, you can't run Chrome's browser sandboxed in Docker containers. There's an environment variable called DOCKER when registering Cuprite (see rails_helper.rb) which tells it to run browser as non-sandboxed.

Alternative solutions

• latest version of Chromium can't run on this old-old-stable version of Debian, which means some tests fail if trying to use old-old-stable Chromium
• You could set the DOCKER environment variable in the dockerfile, but I don't think there's a big difference between that and devcontainer.json,
• Also, you could set cap_add: SYS_ADMIN in docker-compose.yml instead of setting this environment variable which grants the container root access to the parent machine and allows Chrome to run sandboxed, but I think that's overkill

Motivation

I wanted to try out Codespaces because I have a relatively old machine and rspec locally takes about 25 minutes, rspec on Codespaces 4-core takes 10 minutes and is much faster.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

1. Create new codespace from this branch
2. After installation, run bundle exec rspec in terminal. All tests pass.
3. Install Dev Container add-on in VSCode and open repo locally in Dev Container
4. After installation, run bundle exec rspec in terminal. All tests pass.

[awwaiid]

Delightful, thank you!