Assorted CI improvements

• The existing CI jobs can be used to generate reference files for all cards and sequences. They are stored as artifacts.
• Increase number of events in run_physics_efficiency to 5000. This is now set in a variable at the top of .gitlab-ci.yml
• Partly address #257
• Improved throughput reporting #236 (closed)
  • complain about device-averaged throughput decrease exceeding 2.5% - fail the job on detection
  • merge all reports into one message (one for minimal tests, one for the full tests)
  • Ping the pipeline triggerer on mattermost to help increase awareness of the availability of these reports
  • summarised throughput decrease alerts at the top of these messages

To-do

• Needs rebase
• New throughput report can go over the 16k message limit on mattermost
  • try posting separate messages to the same thread to keep things grouped together
• check the GPU_LINK_SPEED is 16x