fix(converter): YAML => KDL conversion with backslash hotkey. (#1879)

* Fixing YAML => KDL conversion with backslash hotkey.

Previously if the hotkey of backslash was used the yaml => kdl
conversion would create a KDL statement like so: `bind "\" {...}`.
That is incorrect kdl syntax since the backslash escapes the following
quote character. A way to get proper KDL is `bind r"\" {...}`. This
commit changes if the old HotKey is a backslash a properly creates KDL
syntax to address the backslash character.

* rustfmt

zellij-client/src/old_config_converter/old_config.rs

@@ -424,7 +424,13 @@ fn keybinds_yaml_to_keybinds_kdl(keybinds_yaml: &OldKeybindsFromYaml) -> String
                         let actions = &key_action.action;
                         let key_string: String = keys
                             .iter()
-                            .map(|k| format!("\"{}\"", k))
+                            .map(|k| {
+                                if k == &OldKey::Char('\\') {
+                                    format!("r\"{}\"", k)
+                                } else {
+                                    format!("\"{}\"", k)
+                                }
+                            })
                             .collect::<Vec<String>>()
                             .join(" ");
                         let actions_string: String = actions