Add dev container

[VeckoTheGecko]

Describe your changes

Adding devcontainers to streamline the installation of an isolated dev environment, that can also be used in GitHub codespaces.

Used this article to help with configuring postcreate/poststart commands.

• postCreateCommand: installs node deps, python deps, and pre-commit hooks (including environment) (tutorial video) (note that the node image is Debian based, coming with Python pre-installed)
• postStartCommand: Runs dev server in background of container (tutorial video)

Related issue number/link

Fixes #340

[VeckoTheGecko]

Thoughts @dmlb? I feel the readme might be getting a little out of hand, so let me know if you have any suggestions :)

[VeckoTheGecko]

Hmmm. Works locally, but not in codespaces.

Getting a Error code: 1302 (UnifiedContainersErrorFatalCreatingContainer) error. Maybe related: https://github.com/orgs/community/discussions/3766

Its not urgent to fix this since we don't have any remote developers (although I might set up later)

[VeckoTheGecko]

Done! 😵😵😵