docs: Add code intelligence troubleshooting guide

Created by: efritz

Fixes https://github.com/sourcegraph/sourcegraph/issues/19361.

Created by: sourcegraph-bot

Notifying subscribers in CODENOTIFY files for diff 3e40f4419ce6dbe0cf324303a672ef3806b9cc87...4571450c90d096962d1e177d75e59199d1b6f4af.

Notify	File(s)
@christinaforney	doc/code_intelligence/img/network-description.png doc/code_intelligence/img/network-waterfall.png doc/code_intelligence/index.md doc/code_intelligence/references/index.md doc/code_intelligence/references/troubleshooting.md