Add warnings when calling deprecated method (#596)

* Add test

* To run the workflow

* Fix import

* Format

* Add warning

* Fix indentation

* Test deprecated method

* More test

* Format

* Add import if needed

---------

Co-authored-by: Adrien Vannson <adrien.vannson@gardacp.com>

src/betterproto/templates/template.py.j2

@@ -84,6 +84,10 @@ class {{ service.py_name }}Stub(betterproto.ServiceStub):
         {% if method.comment %}
 {{ method.comment }}
 
+        {% endif %}
+        {% if method.proto_obj.options.deprecated %}
+        warnings.warn("{{ service.py_name }}.{{ method.py_name }} is deprecated", DeprecationWarning)
+
         {% endif %}
         {% if method.server_streaming %}
             {% if method.client_streaming %}