tenants: add default_locale read only field, pre-hydrate in flows and read in autodetect as first choice

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

authentik/core/templates/if/flow.html

@@ -10,7 +10,9 @@
 <script>ShadyDOM = { force: !navigator.webdriver };</script>
 {% endif %}
 <script>
-window.authentik = {};
+window.authentik = {
+    "locale": "{{ tenant.default_locale }}",
+};
 window.authentik.flow = {
     "layout": "{{ flow.layout }}",
 };