Support hiding attached session

[joshmedeski]

As a user, I want to optionally flag if the attached session should be shown.

• The tmux processSessions function needs to always return the attached session to prevent https://github.com/joshmedeski/sesh/issues/46
• I don't think this should be a global config (just a CLI flag)
• Make it something like --hide-attached for now (not sure if there's an alias that would be clear)
• Hide the zoxide result that matches the attached session? (will cause a bug if someone chooses it)

[markfeinstein]

I can pick this up.