move short-hand aliases from --generate-completion to separate --generate-aliases flag

[Garbaz]

Currently zellij setup --generate-completion zsh includes

function zr () { zellij run --name "$*" -- zsh -ic "$*";}
function zrf () { zellij run --name "$*" --floating -- zsh -ic "$*";}
function zri () { zellij run --name "$*" --in-place -- zsh -ic "$*";}
function ze () { zellij edit "$*";}
function zef () { zellij edit --floating "$*";}
function zei () { zellij edit --in-place "$*";}
function zpipe () { 
  if [ -z "$1" ]; then
    zellij pipe;
  else 
    zellij pipe -p $1;
  fi
}

Equivalently for zellij setup --generate-completion bash and zellij setup --generate-completion bash.

Those are aliases and not completions and in my opinion should not be included in a --generate-completion command.

In particular this is problematic for packaging zellij, as these aliases will end up in the system-wide command namespace, and manually editing the completions file to remove them requires root and is only temporary.

My suggestion with this PR is to move them to a separate --generate-aliases command, though I'd also consider it a valid option to just remove them, since in my opinion short-hand aliases like that should be up to the user to define themselves.