Create devcontainer feature for code-server

[johnstcn]

In order to easily support developing inside devcontainers with no additional required tooling, we need to create an easy way for users to run code-server inside a devcontainer.

Create and publish a Devcontainer feature that will install and run code-server.

We can likely use the desktop-lite feature as a reference (specifically the logic around noVNC): https://github.com/devcontainers/features/tree/main/src/desktop-lite

[DanielleMaywood]

I've created the repo: https://github.com/coder/devcontainer-features