S2I functionality is provided by several modules within the image sources.

modules/s2i/core/modules.yaml has the definition of the environment variables for tuning the S2I build.

Add a new environment variable (defaulting to false) to optionally enable jlink functionality (pick a name)

Most of the S2I implementation lives in      modules/s2i/core/artifacts/opt/jboss/container/s2i/core/s2i-core

 although not all, for example the actual invocation of mvn is here

https://github.com/jboss-container-images/openjdk/blob/edd924a8dd4db529e76fe3b2d6ecc3a71e3c2ccf/modules/maven/default/artifacts/opt/jboss/container/maven/default/maven.sh#L81

figure out the best place to hook the jlink scripts into. It has to take place after mvn completes successfully.