[14.0] group_backend: new module and rename group_backend to base_group_backend

As a developer we have to keep in mind using this module and grant a user with 's group is
equivalent to grant 's group everywhere  has been used.

Co-authored-by: Jean-Charles Drubay <jcdrubay@users.noreply.github.com>

base_group_backend/tests/test_module.py

@@ -0,0 +1,19 @@
+from odoo import Command
+from odoo.tests.common import TransactionCase
+
+
+class TestResUsers(TransactionCase):
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls.base_group_backend = cls.env.ref("base_group_backend.group_backend")
+        cls.internal_user = cls.env.ref("base.user_demo")
+        cls.portal_user = cls.env.ref("base.demo_user0")
+
+    def test_has_groups(self):
+        self.assertFalse(self.portal_user.has_group("base.group_user"))
+        self.assertTrue(self.internal_user.has_group("base.group_user"))
+        self.portal_user.write(
+            {"groups_id": [Command.set([self.base_group_backend.id])]}
+        )
+        self.assertTrue(self.portal_user.has_group("base.group_user"))