[IMP] website: use custom URL for website in backend

The website architecture has been refactored for the internal users and
admins with [1].
Now, they can access the website in the backend inside the website app.
Long story short, the website will be displayed in an iframe in a client
action. The URL of the browser will be tweaked to reflect the iframe one
instead of the real one (which is something like /web#action=..).

It had a few drawbacks:
- On page refresh (F5 or browser button), the user would land on the
  frontend version of the website instead of remaining in the backend.
- When the user edited the URL (Like removing `/shop` and typing `/jobs`
  instead, he would land on the frontend version too.
- Impossible to directly go to the backend version of the website.

Those are improved with this commit by using a slightly different URL
when we are in the backend. A `/@/` will prefix the iframe URL.

If logged in, the user will land on the backend. If not, it will simply
redirect to the frontend version of the website.

[1]: https://github.com/odoo/odoo/commit/31cc10b91dc7762e23b4bde9b945be0c4ce3fe3b

task-2687506

closes odoo/odoo#94580

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/tests/test_controllers.py

@@ -3,6 +3,8 @@
 
 import json
 
+from werkzeug.urls import url_encode
+
 from odoo import tests
 from odoo.tools import mute_logger
 
@@ -44,3 +46,22 @@ class TestControllers(tests.HttpCase):
 
         matching_pages = set(map(lambda o: o['value'], suggested_links['matching_pages']))
         self.assertEqual(set(last_modified_values), set(last_5_url_edited) - matching_pages)
+
+    def test_02_client_action_iframe_url(self):
+        base_url = self.base_url()
+        urls = [
+            '/',  # Homepage URL (special case)
+            '/contactus',  # Regular website.page URL
+            '/website/info',  # Controller (!!also testing multi slashes URL!!)
+            '/contactus?name=testing',  # Query string URL
+        ]
+        for url in urls:
+            resp = self.url_open(f'/@{url}')
+            self.assertEqual(resp.url, base_url + url, "Public user should have landed in the frontend")
+        self.authenticate("admin", "admin")
+        for url in urls:
+            resp = self.url_open(f'/@{url}')
+            backend_params = url_encode(dict(action='website.website_preview', path=url))
+            self.assertEqual(
+                resp.url, f'{base_url}/web#{backend_params}',
+                "Internal user should have landed in the backend")