Prevent secret leaks in source code with GitLab Secret Push Protection

Introduces Secret Push Protection as a generally available feature for GitLab Ultimate and GitLab Dedicated customers. This feature blocks commits containing high-confidence secrets before they are pushed to GitLab, complementing existing Pipeline Secret Detection. It details the risks of leaked secrets, how the feature works by checking commit content, and recommends a layered approach. Configuration steps for enabling the feature per project are provided, along with options to skip push protection and add exclusions. Audit events for various actions related to Secret Push Protection and exclusions are also introduced.