Also set the "locale" option for the keycloak login

With keycloak 9.0 the kcLocale option is gone and the locale selection has been reworked.
If I understand things correctly using the "locale" option should start working with 9.0,
so pass both for now.

See https://www.keycloak.org/docs/latest/server_admin/#_user_locale_selection

Fixes #8

packages/auth/src/keycloak.js

@@ -146,7 +146,8 @@ export class KeycloakWrapper extends EventTarget {
 
         if (!this._keycloak.authenticated) {
             await this._keycloak.login({
-                kcLocale: language,
+                kcLocale: language,  // Keycloak < 9.0
+                locale: language,
             });
         }
     }