USERS.md: add Sportradar
USERS.md: add Sportradar

Signed-off-by: Eric Bailey <ce36984da0bbcea4ccabe54947c0401a080c42f7@sportradar.com>

cilium-team/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,cilium-team/cilium,tgraf/cilium