Allow browsing a specific directory with sessions - #9219

Implementation:

• Interpret a directory argument by listing only *.kitty-session and similar files.
• Reuse the existing sorting logic for the directory chooser and document the workflow.

Flow:

1. User saves all or some sessions to a specific dire, let's say ~/.config/kitty/session.
2. User binds goto_session ~/.config/kitty/session.
3. User invokes the binding and sees a picker, just like the one he would see without providing any arguments in goto_session.