Add __all__ to __init__.py.j2

Author: WiZeYAR

src/asyncapi_python_codegen/generators/amqp/templates/__init__.py.j2

@@ -11,4 +11,6 @@
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License. #}
-from .application import Application
+from .application import Application
+
+__all__ = ["Application"]