允许配置email密码为空 (#2833)

[issue 2577](https://github.com/jumpserver/jumpserver/issues/2577)

apps/settings/serializers.py

@@ -5,7 +5,7 @@ class MailTestSerializer(serializers.Serializer):
     EMAIL_HOST = serializers.CharField(max_length=1024, required=True)
     EMAIL_PORT = serializers.IntegerField(default=25)
     EMAIL_HOST_USER = serializers.CharField(max_length=1024)
-    EMAIL_HOST_PASSWORD = serializers.CharField()
+    EMAIL_HOST_PASSWORD = serializers.CharField(required=False, allow_blank=True)
     EMAIL_FROM = serializers.CharField(required=False, allow_blank=True)
     EMAIL_USE_SSL = serializers.BooleanField(default=False)
     EMAIL_USE_TLS = serializers.BooleanField(default=False)