Use pre-existing JDK installations

I would like to use vfox on github action runners in a way that in case a JDK is already installed vfox does not download the JDK again but the pre-installed one can be registered into vfox.

I would like to be able to do something like this:

# in a initial step I search for installed JDKs and register them with vfox
vfox register java@11-tem /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/11.0.27-6
vfox register java@21-tem /opt/hostedtoolcache/Java_Temurin-Hotspot_jdk/21.0.3

# in later steps I want to call `vfox install java` via some external bash script like this:
vfox install java@11-tem  # should be a no-op since already installed
vfox install java@21-tem  # should be a no-op since already installed
 # query the install dirs of multiple JDKs so I can reference them in Maven's toolchains.xml
JAVA_11_HOME=$(vfox home java@11-tem) 
JAVA_21_HOME=$(vfox home java@21-tem) 

Is this already possible somehow? If not could something like this be added?

Start by tracing the existing vfox register, install, and home commands, using the GitHub Actions JDK paths and java@11-tem/java@21-tem examples in the issue. Determine how registered installations should be recognized by vfox install and exposed by vfox home. Done means pre-existing JDKs are registered without downloading again and their paths can be queried for Maven toolchains.