Goals:

• Decide what is the target Docker base image going forward (e.g AdoptOpenJDK)
• Agent Docker packaging and release is done on trusted CI so that we can integrate it into the automated release flow
• Agent Docker packaging supports multi-platform configuration. See https://github.com/jenkinsci/remoting/pull/292 
• Agent Docker packaging produces multi-architecture Docker images
• The flow is unified for jenkins/slave and jenkins/jnlp-slave so that we have only one build flow instead of manual dependency management
• The release is automatically triggered for updates in parent images
• slave=>agent renaming