Start using Advanced Search in merge request list

Problem to solve

Currently, merge request list page (https://gitlab.com/gitlab-org/gitlab/-/merge_requests) often timeouts if you add a search term.

Proposal

We should start utilizing Advanced Search (if it's possible) for the merge request list. We can start with a simple case when a user provides a search term, no filters, and a sort option we support.

It seems that creating a wrapper for MergeRequestsFinder is unfeasible given that all finders are required to return a scope, and we can't really achieve that given how pagination in Elasticsearch works.