Add a docker compose configuration file

[brettcannon]

As suggested by @malemburg in https://discuss.python.org/t/what-do-people-want-to-see-to-make-supporting-wasi-easier/94472/ , we could add a .devcontainer/compose.yml file to provide another way to get the dev container beyond the instructions in the devguide (which I'm improving). It would probably be something along the lines of:

# Start: docker compose --file .devcontainer/compose.yml up --detach
# Get a shell: docker compose exec cpython-dev bash
# Stop: docker compose down
# Cleanup: docker compose rm cpython-dev
services:
  cpython-dev:
    image: ghcr.io/python/devcontainer:latest
    container_name: cpython-dev
    restart: unless-stopped
    entrypoint: sleep 86400
    working_dir: /workspace
    volumes:
      - ../:/workspace

The biggest benefit I can see from other approaches to using the image outside of GitHub Codespaces like docker run is you don't need to know where the container registry is to get going.

[brettcannon]

And if you want an out-of-tree config extending the config above:

services:
  out-of-tree:
    extends:
      file: compose.yml
      service: cpython-dev
    working_dir: /build
    volumes:
    - ../../build:/build
    - ../:/workspace:ro

The problem with this is if ../../build doesn't exist then it creates it as root when docker compose up runs.

[savannahostrowski]

I finally had time to sit and think about this, and I don't know that this actually makes development simpler. Based on my experience building WASI (and CPython in general), using a Devcontainer via VS Code (i.e., not Codespaces) has been more than sufficient. I'm also not convinced that we need an "editorless" development workflow, given that Devcontainer support is very widespread at this point (it's supported pretty much everywhere and isn't proprietary).

[brettcannon]

Since both Savannah and I came to the same conclusion, I'm going to close this as "won't fix", but if someone else comes along and feels motivated to pick it up then feel free to do so!