🗃️(mailboxes) migrate local part field modification

"+" character was removed from valid character for mailbox creation
this commit adds migration file for database to be up-to-date

src/backend/mailbox_manager/migrations/0012_alter_mailbox_local_part.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.1 on 2024-08-30 10:09
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('mailbox_manager', '0011_maildomain_secret'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='mailbox',
+            name='local_part',
+            field=models.CharField(max_length=150, validators=[django.core.validators.RegexValidator(regex='^[a-zA-Z0-9_.-]+$')], verbose_name='local_part'),
+        ),
+    ]