feat: Add devcontainer

[praateekmahajan]

Makes development easier in vscode world. See https://code.visualstudio.com/docs/devcontainers/containers

Allows folks to contribute more easily as long as they have the Dev Containers extension, they should be able to open the folder as dev container, and it'll create a docker environment without having to setup any env

[if not needed, feel free to close it, this is what I'm trying to use for my development, and I might make changes to dockerfile if I see issues)