Cleaner OFRAK Documentation install in Docker image

[whyitfor]

Which files would be affected? The goal of this work is twofold:

• A user should be able to specify online or offline documentation generation as part of a Docker image build
• Refactor doc generation to avoid awkward code such as https://github.com/redballoonsecurity/ofrak/pull/425#discussion_r1493866997

Does the proposed maintenance include non-doc string functional changes to the Python code? No.

Are you interested in implementing it yourself? Perhaps

[whyitfor]

Note that this overlaps with #454.