We need the same Java version on all Hadoop nodes, but the current CDH release doesn't support Java 11 yet (which Buster has). OTOH we need Buster for some hosts, so create a repository component with a openjdk-8 forwardport for Buster.
openjdk-8 needs openjdk-8 to build, so this needs an intermediate bootstrap build before it can be regularly built on boron.