feat: Shows subcommand aliases in help text

[bigbass1997]

Resolves #918 by utilizing clap's built-in "visible alias" feature. It won't display the aliases exactly as requested in the issue, but I don't believe there's any easy method to format it that way.

Before:

SUBCOMMANDS:
    attach               Attach to a session
    help                 Print this message or the help of the given subcommand(s)
    kill-all-sessions    Kill all sessions
    kill-session         Kill the specific session
    list-sessions        List active sessions
    options              Change the behaviour of zellij
    setup                Setup zellij and check its configuration

After:

SUBCOMMANDS:
    attach               Attach to a session [aliases: a]
    help                 Print this message or the help of the given subcommand(s)
    kill-all-sessions    Kill all sessions [aliases: ka]
    kill-session         Kill the specific session [aliases: k]
    list-sessions        List active sessions [aliases: ls]
    options              Change the behaviour of zellij
    setup                Setup zellij and check its configuration

[a-kenji]

Thank you! This is awesome.