🚸(backend) on user search match emails by Levenstein distance

When the query looks like an email (includes @) we search by
Levenstein distance because we are just trying to prevent typing
errors, not searching anymore.

It is important to still propose results with a short Levenstein
distance because it is frequent to forget a double letter in
someone's name for example "Pacoud" or even "pacou" instead of
"Paccoud" and we want to prevent duplicates or failing on
invitation.

We consider the query string to be an email as soon as it contains
a "@" character. Trying harder to identify a string that is really
an email would lead to weird behaviors like toto@example.gouv looking
like and email but if we continue typing toto@example.gouv.f not
looking like an email... before toto@example.gouv.fr finally looking
like an email. The result would be jumping from one type of search
to the other. As soon as there is a "@" in the query, we can be
sure that the user is not looking for a name anymore and we can
switch to matching by Levenstein distance.

src/backend/core/migrations/0013_activate_fuzzystrmatch_extension.py

@@ -0,0 +1,16 @@
+# Generated by Django 5.1.4 on 2025-01-25 08:38
+
+from django.db import migrations
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0012_make_document_creator_and_invitation_issuer_optional'),
+    ]
+
+    operations = [
+        migrations.RunSQL(
+            "CREATE EXTENSION IF NOT EXISTS fuzzystrmatch;",
+            reverse_sql="DROP EXTENSION IF EXISTS fuzzystrmatch;",
+        ),
+    ]