Added information how to run integration tests against Confluence stack

Instructions in README.rst
Docker Compose file to start the Confluence stack

README.rst

@@ -166,6 +166,23 @@ create a configuration template with the correct working directory.
 The integration tests are run in parallel e.g. in the CI-pipeline.
 The tests need to be engineered taking this in mind.
 
+Since the integration tests run against a Kafka cluster, Kafka REST and Kafka Schema Registry using
+their APIs, it's possible to run them not only against Karapace that the tests internally
+setup and teardown but against long-running services. This allows you to start
+Karapace independently from the integration tests and e.g. inspect Kafka contents after the tests have run.
+
+The integration tests can be configured to use a running (ZooKeeper),
+Kafka (:code:`--kafka-bootstrap-servers`), Kafka REST (:code:`--rest-url`)
+and Schema Registry (:code:`--registry-url`), e.g. like this::
+
+    python -m pytest -vvv --registry-url http://127.0.0.1:8081 --rest-url http://127.0.0.1:8082/ --kafka-bootstrap-servers 127.0.0.1:9092 tests
+
+You can run the integration tests against Kafka REST and Schema Registry from Confluent.
+You can freely start these services before running the tests however you wish, but for convenience
+you can use the provided Docker Compose file to start ZooKeeper, Kafka, Kafka REST and Schema Registry::
+
+    docker-compose -f tests/integration/confluent-docker-compose.yml up -d
+
 There are several coding style checks in `GitHub Actions <https://github.com/aiven/karapace/actions>`_.
 Your code changes need to pass these tests. To run the checks locally,
 you can run them manually::

tests/integration/confluent-docker-compose.yml

@@ -0,0 +1,52 @@
+---
+version: '2'
+services:
+  zookeeper:
+    image: confluentinc/cp-zookeeper:latest
+    hostname: zookeeper
+    ports:
+      - "2181:2181"
+    environment:
+      ZOOKEEPER_CLIENT_PORT: 2181
+      ZOOKEEPER_TICK_TIME: 2000
+
+  kafka:
+    image: confluentinc/cp-kafka:latest
+    hostname: kafka
+    depends_on:
+      - zookeeper
+    ports:
+      - "9092:9092"
+      - "9101:9101"
+    environment:
+      KAFKA_ZOOKEEPER_CONNECT: 'zookeeper:2181'
+      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
+      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://kafka:29092,PLAINTEXT_HOST://localhost:9092
+      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
+      KAFKA_CONFLUENT_SCHEMA_REGISTRY_URL: http://schema-registry:8081
+
+  schema-registry:
+    image: confluentinc/cp-schema-registry:6.1.1
+
+    hostname: schema-registry
+    depends_on:
+      - kafka
+    ports:
+      - "8081:8081"
+    environment:
+      SCHEMA_REGISTRY_HOST_NAME: schema-registry
+      SCHEMA_REGISTRY_KAFKASTORE_BOOTSTRAP_SERVERS: 'PLAINTEXT://kafka:29092'
+      SCHEMA_REGISTRY_LISTENERS: http://0.0.0.0:8081
+
+  rest:
+    image: confluentinc/cp-kafka-rest:latest
+    depends_on:
+      - kafka
+    ports:
+      - "8082:8082"
+    environment:
+      KAFKA_REST_HOST_NAME: confluent-rest
+      KAFKA_REST_BOOTSTRAP_SERVERS: 'kafka:29092'
+      KAFKA_REST_LISTENERS: "http://rest:8082"
+      KAFKA_REST_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081'
+