Create Devcontainer build

[bennothommo]

This PR introduces the ability for Winter to run in a development container, which is basically a pre-constructed configuration for Docker that creates a fully-functional development environment for Winter. It is supported by VSCode, PHPStorm and many other editors to easily create local development copies, and also allows us to use GitHub Codespaces to test PRs or make edits to the core directly in GitHub.

A more thorough explanation can be found in the README for the dev container configuration.

[bennothommo]

Here's how it looks in GitHub Codespaces:

[LukeTowers]

@jaxwilko do you have any input?

@bennothommo does the .devcontainer folder get included when creating winter projects with composer?

[bennothommo]

@LukeTowers currently, yes it would. I'm in two trains of thought on whether to keep it for Composer installs - on the one hand, using Composer would imply they have a working dev environment (or at least PHP). On the other hand, it's still quite useful for getting a project off the ground quickly without having to bootstrap it.

It might be worth stripping it out for installs through the Web Installer though.

[jaxwilko]

@LukeTowers Looks cool to me, I generally just spin up my own containers and probably wouldn't use the one provided here but I can see the value for some people.

@bennothommo I would lean more to excluding it when installed with composer, generally if somebody has php install then they probably have it set up... or can run the php built-in web server. Perhaps it should only be downloaded when cloning the repo (i.e. not in the web installer or via composer).

[bennothommo]

I'll merge this now as it's a developmental change that won't affect anyone else. We can tweak if we need to, down the line.