Update to NGINX Ingress 1.15
<!--
NOTICE: This Issue tracker is for the GitLab Helm chart, not the GitLab Rails application.
Support: Please do not raise support issues for GitLab.com on this tracker. See https://about.gitlab.com/support/
-->
## Summary
NGINX Ingress just released it's last minor release 1.15 before its official retirement. While GitLab chart will disable NGINX Ingress in 19.0, we should update to the latest release for now.
## Acceptance Criteria
- [ ] Images mirrored
- [ ] Mirror updated and UBI/FIPS variants have been built
- [ ] Chart updated
issue