Split CLI to subcommands (and migrate to picocli)

Plugin Installation Manager Tool implements multiple commands at the moment, and options are a bit confusing. The tool would benefit from sub-commands (`install-plugins`, `list-updates`) that could simplify the interface for users and allow to easily extend it going forward.

Such a migration would also allow using Plugin Installation Manager as a subcommand on its own, e.g. inside Jenkinsfile Runner CLI which needs plugin management.

FTR https://groups.google.com/g/jenkinsci-dev/c/jTkOpdZ7z1s for the discussion. Reference migration: https://github.com/jenkinsci/jenkinsfile-runner/pull/432