Add a runbook for predictive tests
Context
Related to gitlab-org/gitlab#405026 (closed)
https://about.gitlab.com/handbook/engineering/quality/engineering-productivity/#predictive-test-jobs-via-test-mapping describes predictive tests in a high-level overview, but I felt like a more technical, in-depth documentation was missing for the people operating this part of the CI/CD pipelines.
What's in this MR?
This MR adds a RUNBOOK for predictive tests, to explain what they do and how they work.
Edited by David Dieulivol