[RTADPA BW Tests] Assorted improvements to monitoring pages
This MR is a follow up from !4419 (merged), and addresses several of the points collated in lhcb-datapkg/PRConfig#41.
In particular:
- Refactor
combine_rate_output.pyandmake_bandwidth_test_page.pyfor readability and clarity - Add a summary table to the top of monitoring histogram pages
- Organise the monitoring histogram pages by working group
Edited by James Connaughton
