Rename t to tmux-sessionizer

This matches ThePrimeagen's script that mine is based on and that I'll
probably switch to in the future.

I've added to the Nix store as custom-tmux-sessionizer so it doesn't
conflict with the tmux-sessionzer packages that's already in the store.

nix/modules/home-manager/features/cli/tmux.nix

@@ -72,8 +72,7 @@ in
         set-option -g pane-active-border-style "fg=#1f2335"
         set-option -g pane-border-style "fg=#1f2335"
 
-        bind-key -r f run-shell "tmux new-window t"
-
+        bind-key -r f run-shell "tmux new-window custom-tmux-sessionizer"
 
         if-shell "[ -f ~/.tmux.conf.local ]" 'source ~/.tmux.conf.local'
       '';