Update policies docs to mention merge request pipelines
What does this MR do and why?
This MR updates "Merge request approval policies" documentation to mention the fact that latest
security templates are required with merge request pipelines.
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Related to #428173 (closed)
Edited by Martin Čavoj