Monorepo troubles doc

Created by: DaedalusG

This is a (very) rough draft for a PR intended to give folks with monorepos an idea about why monorepos cause specific problems. Its very much in a draft state and I think it could use a better look particularly in terms of the code links. Sharing now to get some insights from the search-core and codeintel teams about the validity of the information contained here (especially the code links 😅 . Hoping this can be instructive to customers and team members alike till we can rollout improvements search-core is working on.

TL;DR features that default to unindexed symbols search when a zoekt index search is considered stale are likely to default because monorepos usually receive frequent commits. In these cases, gitserver and symbols try to lazily respond and this can result in timeouts or long waits for results. Our current best answer for this is please give gitserver and symbols more CPU.

I believe I've identified the most common frustrations here, but the codeintel one is a little dubious.