Update EPEL package request to add clarity for existing maintainers and releng
    
    For consistency in handling EPEL package requests, document needed steps
    for existing maintainers and for releng.
    
    Also make the request templates more consistent between regular
    packagers and EPEL Packagers SIG members.
    
    Finally, put an advisory note to not request access via the SIG route
    for now while the workings are being reviewed.
    
    Signed-off-by: Michel Lind <salimma@fedoraproject.org>