Add support for variant in the new RHCOS pipeline to be able to create a stream for each variant available in each branch.

Draft of suggested steps:
1. Try a local RHCOS 9 build
2. Push a branch for the pipeline config + pipeline code with minor changes
3. Setup the devel pipeline to use those branches
4. Add new streams for RHCOS 9 on 4.13 first
5. Add code to handle variants
6. Fix bugs as needed
7. Enable for 4.12