Add and document option for enabling email lookup (#913) * Docs: Document option for enabling email lookup * Add the new config in the config files * Apply suggestions from code review Co-authored-by: Ieva <ieva.vasiljeva@grafana.com> * Don't capitalize identity providers * Apply suggestions from code review Co-authored-by: Jo <joao.guerreiro@grafana.com> * Apply suggestions from code review Co-authored-by: Christopher Moyer <35463610+chri2547@users.noreply.github.com> --------- Co-authored-by: Ieva <ieva.vasiljeva@grafana.com> Co-authored-by: Jo <joao.guerreiro@grafana.com> Co-authored-by: Christopher Moyer <35463610+chri2547@users.noreply.github.com> (cherry picked from commit 8380bc7d6a79794cc260bf1c427e2b4e849adbf6)