KR: Dogfood feature to selectively run test in GitLab merge requests workflow => 95%

Plan

• Identify stakeholders to collaborate with (Infra, Eng Productivity, Development (Testing group)
• Have a communication plan in place when we enable it in CI, this will affect merge times (quicker or slower)
• Work with the counterparts in defining the change in our CI files where this will only be enabled for unit tests.
• Enable it for a short period of time and evaluate.
• Summarize findings and give feedback to the development and product teams. gitlab-org/gitlab#222706 (closed)
• Make decision if this should be a permanent addition to our CI configuration.