Standardised dev commands in a `Makefile`

[alcarney]

This is an initial attempt at moving to a standardised development environment based on a devcontainer. The container itself is nothing special - just a Ubuntu container that provides a known starting point.

The rest is then built up using a series of Makefile definitions, so assuming you have access to make, curl, tar and maybe a few other standard utilities it should be possible to rely on just the Makefiles - but I can't guarantee that.

Running make watch, from the code/ folder should be enough to bootstrap the environment needed to work on the VSCode extension

[alcarney]

This is going to be a gradual process, I tried launching the VSCode extension via the devcontainer.... and nothing worked! :man_facepalming: There's obviously more to using devcontainers than just building an image with the right set of tools in it.

However, having some common tasks automated is a good start! :)