Merge branch '479145_manage_billable_promotion_known_issues' into 'master'

Add Known Issues for Manage Billable Promotions

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/168180



Merged-by: Lorena Ciutacu <lciutacu@gitlab.com>
Approved-by: Lorena Ciutacu <lciutacu@gitlab.com>
Reviewed-by: Lorena Ciutacu <lciutacu@gitlab.com>
Co-authored-by: Suraj Tripathi <stripathi@gitlab.com>