codeintel: Auto index Go deps of sg/sg on Cloud

Created by: efritz

Auto-indexing is only enabled on Cloud; this adds a specific check for sg/sg and will enqueue all of the deps in the root go.mod file. This will cheaply simulate what it would be like to have support for dependency indexing in a Go project.

Will want to merge ideas with Olaf to make a system that can support languages in a generic way (not ad-hoc per language).