Added the advanced_context_resolver feature flag

What does this MR do and why?

The MR adds a new feature flag :advanced_context_resolver. This is the first flag in the product which won't be used in monolith for now, but aims at the IDEs.

This flag is supposed to protect the efforts in Advanced Code Context Resolver Architecture - (... (gitlab-org/editor-extensions&55) about advanced context resolution in IDEs when working with AI.