Open-up mock queues

⭐️ Features

• Add access to messages in mock queues (#87)
• Add FOSSA check

🐞 Bug fixes

• Fix MetricsCollector#consumedMessage invocation order (#117)
• Requeue unacked messages delivered to a consumer when it is cancelled (#96)

🔨 Dependency upgrades

• integration-test
  • micrometer-core to 1.5.1
  • spring-rabbit to 2.2.7.RELEASE
• test
  • mockito-core to 3.3.3
  • junit-jupiter to 5.6.2
  • assertj-core to 3.16.1
• maven
  • pitest-maven to 1.5.2
  • maven-javadoc-plugin to 3.2.0