Please support plugin to generate java runtime for Java application

[vpa1977]

What needs to get done

Java runtime plugin generates java runtime using jdeps/jlink tools.

Prerequisites:

• JDK is installed in the build image
• ca-certificates-java installed in the build image
• Application Jar files are located in $CRAFT_STAGE/jars/

Operations:

• unpack jar files to a temporary location
• Build classpath using jars found in temporary location (spring packages dependencies under BOOT-INF/
• run jdeps against jars in $CRAFT_STAGE/jars/ using classpath from the step above
• run jlink and deploy image into /usr/lib/jvm/java--openjdk-
• link java under /usr/bin/java
• java cacerts copied into staging area and symlinked to openjdk

Why it needs to get done

Jlink allows to link lean Java runtime images that only contain components of Java runtime required by the application.
Java provided by Ubuntu archive contains all the modules in lib/modules file (200mb). This can go down to as small as 27mb for java.base.
This both reduces attack surface of the Java application and reduces the deployment size.