Refactor Docker setup to support separate dev/test and prod images, similar to Bedrock

[stevejalim]

Once #782 is done, we will have separate prod and dev requirements files. It would be good to leverage these to make our prod build smaller and with no unnecesary dependencies.

To acheive this, we will need to refactor our Docker setup for Basket, to generate a Dev/Test image separate from the main/Prod image and to use these as appropriate

Success criteria

• Current container/image workflow is understood
• Workflow is updated to generate dev-and-test-specific and prod-specific builds
• Prod build still gets shipped to basket-production and basket-staging
• Dev/Test build gets shipped to basket-dev
• CI is still happy