Add full namespace descendants cache

Pavel Shutsinrequested to merge
add_descendants_ids_to_hierarch_cache into master

What does this MR do and why?

Add full namespace descendants cache

This cache can be used to retrieve full namespace hierarchy including ProjectNamespaces.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Merge request reports