Research obvious endpoint gaps and create issues to add coverage in the Performance Toolkit

We should aim to add tests that cover at least all of the common endpoints (API) for GitLab.

• One list we derived from a customer can be found here - https://docs.google.com/spreadsheets/d/1m1Jpk6nFf4FnIp47-GwJ84iFuk1FTeLGGe2CBNR5e50/edit#gid=0
• Recent customer top API list - https://gitlab.com/gitlab-org/quality/performance/issues/65#note_215898596
• Other endpoints needs to be found out by finding the right people who can provide this / seeing what customers or users say. e.g. This Hackernews thread for example called out code search (Search API Docs)

Task then is to find out what endpoints are commonly used today (and how to best find out this info), if they are covered in the tests and add tests for ones that aren't.

Note that to complete this specific issue we're only looking for straightforward endpoints to be added that can be covered with existing datasets and for other endpoints that require more complex setup or data to be added we should raise individual issues.