Automated performance tests (beginning load --> render)

- We have this, understand how to utilise here
- Benchmarking over time
- Background loading times independent of UI specific loading

Relates to #6647

Note: For this to be useful, we need to make the environment and outputs more consistent

The issue names no files, tests, or entry points. Start by reviewing related issue #6647 and the existing performance-test setup; done should include automated beginning-load-to-render benchmarks with consistent environments and outputs that can be compared over time.

Written by the indexing model from the issue text.