Neo-Tree Improvements

[mehalter]

Neo-tree has added window picker keybindings which require a window-picker to be installed. This adds one and fully lazy loads it on it's module. If the user never uses the keybinding then the plugin never loads.

This also adds an auto command that will auto close AstroNvim if a window is closed and only Aerial and Neo-tree are opened.

Resolves #733

[github-actions]

Use the following updater settings in your user/init.lua file, restart, and run :AstroUpdate to test this pull request:

  updater = {
    channel = "nightly",
    branch = "window_picker",
  },