Add "space" key to bind in vi normal mode (#6590)

* Add "space" key to bind in vi normal mode

Implements #6586

No special logic to prevent you from binding it in other modes!
Needs a separate change to reedline to make it available in the default
listing of `keybindings list`.

* Update reedline to report the available `space`

Pulls in nushell/reedline#486

crates/nu-cli/src/reedline_config.rs

@@ -666,6 +666,7 @@ fn add_parsed_keybinding(
 
             KeyCode::Char(char)
         }
+        "space" => KeyCode::Char(' '),
         "down" => KeyCode::Down,
         "up" => KeyCode::Up,
         "left" => KeyCode::Left,