Merge branch 'stable-3.6' into stable-3.7

* stable-3.6:
  Register Kafka consumers with external groupId when plugin starts
  Make KafkaBrokerApi class implement ExtendedBrokerApi interface
  Consume events-broker from source
  Add validation dependency on events-broker module
  Add .gitignore file in the project
  Pass correct amount of arguments to Malformed event log line
  Add Kafka REST API authentication
  Fix the topic events replay Kafka REST-API
  Use Kafka REST Proxy id to subscribe to the correct instance
  Fix Kafka REST Proxy accepts header for topic meta-data
  Kafka REST Client: avoid clashes between clients
  Fix threshold of HTTP wire logging
  Delete subscription at the end of ReceiverJob
  Update kafka-client 2.1.0 -> 2.1.1
  Increase patience to 30s for shouldReplayAllEvents test
  Remove unused RequestConfigProvider
  REST ClientType: Make thread pool and timeouts configuration
  Extract configuration properties into constants
  Manage Kafka clientType when starting session
  Receive messages through Kafka REST API
  Send messages through Kafka REST API
  Abstract Publisher/Subscriber into generic interfaces
  Wait at most for 5s for an empty topic
  Assert that messages are acknowledged in KafkaBrokerApiTest
  Add Kafka REST-API container in test
  Remove access to deprecated poll(long) method
  Use explicit Kafka image:tag in tests
  Do not connect KafkaSession without bootstrap servers

Change-Id: Icd9e8f52e97fa18662350b3508dd57c35d5db753