Allow using only mirror param for updates and update documentation

What does this MR do and why?

This change is to:

• allow the mirror parameter to be used without needing to include other parameters
• update documentation with examples for configuring pull mirrors

How to set up and validate locally

Try following the documentation and see the projects can be configured for pull mirroring

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #356154 (closed)