🐛(core) fix AccountService api_key field declaration

Override save is a better way to auto generate api_key if
it is not set.
Default with random secret generate a new migration each time we
run `make makemigrations`.

src/backend/core/migrations/0015_alter_accountservice_api_key.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.1.8 on 2025-04-10 07:19
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0014_accountservice'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='accountservice',
+            name='api_key',
+            field=models.CharField(max_length=255, verbose_name='api key'),
+        ),
+    ]

src/backend/core/models.py

@@ -1107,7 +1107,6 @@ class AccountService(BaseModel):
     api_key = models.CharField(
         _("api key"),
         max_length=255,
-        default=secrets.token_urlsafe(32),
     )
     scopes = ArrayField(
         models.CharField(max_length=255, validators=[validate_account_service_scope]),
@@ -1123,6 +1122,14 @@ class AccountService(BaseModel):
     def __str__(self):
         return self.name
 
+    def save(self, *args, **kwargs):
+        """
+        Override save method to generate a new api_key if it is not set.
+        """
+        if not self.api_key:
+            self.api_key = secrets.token_urlsafe(32)
+        return super().save(*args, **kwargs)
+
     @property
     def is_authenticated(self):
         """Indicate if the account service is authenticated."""