Merge request search has a high number of database calls

Summary

There is a high number of calls to the database when loading merge request search results.

Steps to reproduce

1. enable the performance bar
2. perform a global merge request search: ## Summary

There is a high number of calls to the database when loading project search results.

Steps to reproduce

1. enable the performance bar
2. perform a global project search: https://gitlab.com/search?scope=projects&search=test
3. for the search I performed, there were 153 postgres calls

What is the current bug behavior?

There are some (undetected) N+1 calls for merge requests search results

Possible fixes

• Web UI preloads from SearchController are using with_web_entity_associations from the merge request model
• merge request view is rendered using HAML: app/views/search/results/_merge_request.html.haml
• N+1 specs are likely missing data setup (for whatever data is causing the excessive queries):
  • spec/requests/search_controller_spec.rb
  • ee/spec/requests/search_controller_spec.rb