Update dev container

[Scotchester]

⚠️ base branch: feature/appcontainer ⚠️

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PR 3 of ??

This PR updates the dev container config that we started with from template-devcontainer to:

• Updates the dev container config to build from app container
• Adds debugging/testing support in VS Code
• Adds Python code quality tooling

Testing

If you've already successfully tested PR #2 (the bare app container), the application can now be run in the devcontainer. On this branch

1. Rebuild and Reopen in Container
2. Use F5 or the UI to initiate a debug session

You should see output in a new terminal indicating that the app is now running, and you should now be able to invoke it in your Slack test workspace! Try the /define command to confirm.

You can also now use the VS Code Testing pane to run the tests.

Other notes

• I again borrowed heavily from how Benefits approached its dev container setup, though I didn't get as fancy with the pyproject.toml. Not sure if there's value in packaging this one up in the same way as Benefits?
• This PR would be a good starting point for some of the things in chore(pre-commit): autoupdate hooks template-devcontainer#11

[Scotchester]

I changed this from postAttachCommand to postCreateCommand after stumbling into this old SO thread that Aidan Feldman had commented on a while ago. I can't recall what minor build issue led me there, but I got past it.

Anyway, a commenter suggested that postCreate would be better since it should only need to run once when the devcontainer is (re)built. This works fine for me, but I admittedly didn't look into it any further to see if there's a reason we wouldn't want to do it post-create.

[Scotchester]

This was a trick needed to get this to install on Alpine (in addition to installing node and npm in the Dockerfile).

[Scotchester]

8001 matches what the Benefits does. I think switching to 8001 in template-devcontainer would be worthwhile, since 8000 is the default port for a lot of services that might be run for the primary purpose of your dev container.