RFC: Implement code intelligence for gitlab-org/gitlab

The scaling issue has been discussed #202189 (closed) and even though we haven't seen it in action yet, it seems as if we're on the right track!

One of the issues that prevent us from having code intelligence on gitlab-org/gitlab is that there's no library which indexes a Ruby project into LSIF file: https://lsif.dev/

The popular libraries provide LSP servers for code intelligence, but they don't provide a way to generate LSIF

• https://github.com/castwide/solargraph
• https://github.com/sorbet/sorbet
• https://microsoft.github.io/language-server-protocol/implementors/servers/

Sourcegraph uses basic code intelligence for Ruby https://sourcegraph.com/extensions/sourcegraph/ruby

Apparently, we need to create our own solution for indexing a Ruby project (or work it around). Not necessarily the one which generates a valid LSIF file, but at least the one which conforms with our parsing logic