reorganization of _examples and add some new examples such as iris+groupcache+mysql+docker

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/kafka-api/docker-compose.yml

@@ -0,0 +1,29 @@
+version: '3.1'
+
+services:
+  zookeeper:
+    image: wurstmeister/zookeeper
+    ports:
+      - 2181:2181
+  kafka:
+    image: wurstmeister/kafka
+    ports:
+      - 9092:9092
+    environment:
+      KAFKA_ADVERTISED_HOST_NAME: 10.122.1.109 # replace that with your own local ipv4 addr.
+      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
+  # kafka:
+  #   image: confluentinc/cp-kafka:5.5.0
+  #   hostname: kafka
+  #   ports:
+  #     - 9092:9092
+  #   environment:
+  #     KAFKA_ADVERTISED_LISTENERS: LISTENER_DOCKER_INTERNAL://kafka:19092,LISTENER_DOCKER_EXTERNAL://${DOCKER_HOST_IP:-127.0.0.1}:9092
+  app:
+    build: .
+    ports:
+      - 8080:8080
+    environment: 
+      KAFKA_1: kafka:9092
+    depends_on:
+      - kafka