Docs: Auditing updates (#30433)

* Docs: reformat auditing table

* Docs: update auditing log format section

* fix SAML SLO link in auditing doc

* Apply suggestions from code review

Co-authored-by: Ursula Kallio <73951760+osg-grafana@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Ursula Kallio <73951760+osg-grafana@users.noreply.github.com>

* update user field desc

Co-authored-by: Ursula Kallio <73951760+osg-grafana@users.noreply.github.com>