Zoekt project search should select correct zoekt node instead of first node for namespace

For the project-level search when the search with a replica is enabled, we are fetching the zoekt_nodes.first https://gitlab.com/gitlab-org/gitlab/-/blob/8530bfaeaddb197d235bd5efa9d12f720527483b/ee/app/services/concerns/search/zoekt_searchable.rb#L35 , which might be wrong when a namespace is split among multiple nodes. Select the correct zoekt_node for the project-level search