Follow-up to JENKINS-51710

• Ready-to-fly demo:
  • We start master instance with preconfigured agent and Kafka (e.g. via Configuration-as-Code plugin)
  • Docker Compose starts preconfigured Master and agent instance, they connect automatically
  • There few demo jobs in the instance so that a user can launch a job on the agent
  • It may require some self-configuration of the Jenkins instance (automatic demo creation)