Default branches on different namespaces
    
    Changes after the migration from 'master' branches.
    Default branches for namespaces:
     * 'rpms', 'container', 'modules' - branch 'rawhide'
     * 'flatpaks'  - 'stable'
     * 'tests' - 'main'
    
    Fixes: #428
    JIRA: RHELCMP-4161
    Merges: https://pagure.io/fedpkg/pull-request/430
    
    Signed-off-by: Mohan Boddu <mboddu@bhujji.com>