Package shell completion into DEB and RPM

[jzelinskie]

Right now only homebrew is shipping shell completion:

$ dpkg -c zed_0.16.4_linux_amd64.deb 
drwxr-xr-x root/root         0 2024-01-22 16:10 ./usr/
drwxr-xr-x root/root         0 2024-01-22 16:10 ./usr/bin/
-rwxr-xr-x root/root  27877376 2024-01-20 01:11 ./usr/bin/zed