Undercoverage has some unexpected side effects that cause frequent developer friction/confusion which need to be remediated to ensure that test coverage does not decrease through MR changes. Confusion with `rspec:undercoverage` is increasing and [rate of ~"pipeline:skip-undercoverage" has increased to 1.4% of all MR pipelines](https://app.periscopedata.com/app/gitlab/590833/WIP:-Kyle-Wiebers-Scratchpad?widget=14702104&udv=0)  This goal of this spike is to reduce the confusion from these bugs. ### Known causes of failures - Minimal CI does not run the job in question: https://gitlab.com/gitlab-org/gitlab/-/issues/363061 - Potential flaky specs re-run in rspec jobs overwrite simplecov data: https://gitlab.com/gitlab-org/gitlab/-/issues/365379 - SimpleCov doesn't generate the correct coverage data - `rspec:coverage` does not merge the multiple coverage files from `paralllel` execution correctly - `rspec:undercoverage` not using the coverage data correctly