Update rpm-repos-openSUSE to rev 5 via SR 897704
https://build.opensuse.org/request/show/897704
by user Pharaoh_Atem + dimstar_suse
- Add missing GPG key references to Leap base repositories
- Add missing SLE and Backports repositories for Leap 15.3+ (boo#1186593)
- Rework GPG key file setup to use files from openSUSE-build-key