Add support for override_project_ci strategy in PEP

What does this MR do and why?

This MR is a proposal for override_project_ci policy strategy. Based on the requirements in Pipeline Execution Policy Type (&13266):

In Override mode, the project CI configuration will be ignored and replaced with the policy CI configuration.

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.

Screenshots or screen recordings

inject_ci strategy (default)	override_project_ci strategy

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Related to #455261 (closed)