Add unit tests for authentication and webhook parsing

- Implement tests for basic and bearer authentication headers in `test_auth.py`.
- Create tests for the `EasybillWebhookParser` in `test_webhooks.py`, covering JSON and form-encoded payloads, as well as a generic parse and acknowledgement method.

generated/sync/docs/DiscountPositionGroup.md

@@ -0,0 +1,33 @@
+# DiscountPositionGroup
+
+
+## Properties
+
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**id** | **int** |  | [optional] [readonly] 
+**customer_id** | **int** |  | 
+**discount** | **int** | The discount value depending on \"discount_type\". If not provided, inherits from customer when available | [optional] 
+**discount_type** | **str** | AMOUNT subtracts the value in \"discount\" from the total<br/> QUANTITY subtracts the value in \"discount\" multiplied by quantity<br/> PERCENT uses the value in \"discount\" as a percentage<br/> FIX sets the value in \"discount\" as the new price. If not provided, inherits from customer when available | [optional] [default to 'PERCENT']
+**position_group_id** | **int** |  | 
+
+## Example
+
+```python
+from easybill_generated_sync.models.discount_position_group import DiscountPositionGroup
+
+# TODO update the JSON string below
+json = "{}"
+# create an instance of DiscountPositionGroup from a JSON string
+discount_position_group_instance = DiscountPositionGroup.from_json(json)
+# print the JSON string representation of the object
+print(DiscountPositionGroup.to_json())
+
+# convert the object into a dict
+discount_position_group_dict = discount_position_group_instance.to_dict()
+# create an instance of DiscountPositionGroup from a dict
+discount_position_group_from_dict = DiscountPositionGroup.from_dict(discount_position_group_dict)
+```
+[[Back to Model list]](../README.md#documentation-for-models) [[Back to API list]](../README.md#documentation-for-api-endpoints) [[Back to README]](../README.md)
+
+