API docs: MVP/barebones webapp frontend for Go

Created by: slimsag

Depends on:

• API docs: scope out initial project implementation (#19385 (closed))
• API docs: define rough user experience, workflows (#19386 (closed))
• API docs: figure out exact data requirements from LSIF (#19387 (closed))
• API docs: propose LSIF extensions (#19388 (closed))
• API docs: implement LSIF extensions for Go LSIF indexer / langserver (#19395 (closed))

At this point, we would have the data we need from LSIF but will need to put together an actual webapp frontend for Go API docs, i.e. "draw the rest of the owl".

This issue would be closed as soon as we have any basic version of functioning Go docs on sourcegraph.com, limited to just the Sourcegraph org if needed. Then, we will file follow-up issues and prioritize accordingly, which may be where the most substantial amount of time is spent before being able to say "we've done it" for Go.

For the general idea of how this would function from a product UX point of view, see: API docs: product UX, LSIF investments, layout challenges, implementation roadmap