Show docs in split view in UI

Problem

We rely on docs quite a bit since GitLab is a complex product. A lot of the time I end up opening several tabs and losing my place when switching between them all.

Proposal

Add an option for split view viewing of relevant docs.

📽️ Initial walkthrough

🎨 Figma

	Screen_Recording_2021-02-10_at_1.31.54_PM