search contexts: refactor auto-defined contexts suggestions

Created by: novoselrok

This PR refactors fetching auto-defined search contexts on the client including the suggestions. It refactors fetching auto-defined search contexts into a function. Previously it was defined as a "cached" observable which fired frequently when moving between pages and it caused a lot of failed/weird requests in the network tab. It was also used to return auto-defined search context suggestions separately from user-defined contexts. This is now removed, and all suggestions for search contexts are coming from the backend.