contrib: Optimize extract_authors.sh script
contrib: Optimize extract_authors.sh script

By using built-in formatting primitives instead of independently
fetching names and emails from git in separate commands, we can reduce
git history iteration by 50%, saving 30s per authors update on my
system.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@cilium.io>

cilium/cilium,michi-covalent/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium