Database schema diff 12 - A different index name: index_forked_project_links_on_forked_to_project_id (source) vs forked_project_links_forked_to_project_id_key (production)

Issue to address database schema difference 12 in https://gitlab.com/gitlab-org/gitlab-ce/issues/51438#current-differences

A different index name: index_forked_project_links_on_forked_to_project_id (source) vs forked_project_links_forked_to_project_id_key (production)