Add missing confluent base class

diagrams/confluent/__init__.py

@@ -0,0 +1,12 @@
+"""
+Confluent provides a set of services for the Kafka ecosystem.
+"""
+
+from diagrams import Node
+
+
+class _Confluent(Node):
+    _provider = "confluent"
+    _icon_dir = "resources/confluent"
+
+    fontcolor = "#ffffff"