Idea: Docker build arg for Python dev dependencies

[bufke]

Description

Sometimes it's nice to have dev dependencies installed in docker:

• A developer running locally
• A CI script that runs a dev-only tool, such as pytest
• e2e test (requires mongomock)

Other times it's not

• Production builds
• CI builds where it isn't necessary and slows it down

A docker build arg would provide a means to control dev dependency installation at build time. Services like kobo compose or ci scripts could enable these by default as needed by the use case.

Advantages

• For local dev, pytest just works. No special install step.
• Perhaps slightly faster CI build steps
• Ease of end to end testing set up

Disadvantages

• Docker build can result in two different results, which adds complexity

A question raised is - is it bad to offer different dependencies for production/dev? I think this isn't related. When I run pytest, I must install the dev dependencies. So this is already happening and the build arg is not related.