[RTADPA BW Tests] Monitoring histogram improvements

Follow up from lhcb/Moore!4419 (merged)

• Summary at top of monitoring page lhcb/Moore!4419 (comment 9199741) [Addressed in lhcb/Moore!4711 (merged)]
• Organise main monitoring page [Addressed in lhcb/Moore!4711 (merged)]
• Make all pages and descriptions in make_bandwidth_test_page.py lhcb/Moore!4419 (comment 9199747) [Addressed in lhcb/Moore!4711 (merged)]
• Improve add_link function in make_bandwidth_test_page.py [Addressed in lhcb/Moore!4711 (merged)]
• Simplify make_html_for_single_test lhcb/Moore!4419 (comment 9200859) [Addressed in lhcb/Moore!4711 (merged)]
• Reinstate the monitoring subdirectory (likely requires Handler changes)
• Investigate options.output_level to suppress monitoring logs in Moore