log4j includes different class files for different jvm versions. This
means our uberjar includes these versions so we are a multi-release
jar. Need to set this in our manifest.

Fixes the reflection warning seen on startup on jdk 11's

~/p/w/metabase ❯❯❯ java -jar target/uberjar/metabase.jar
WARNING: sun.reflect.Reflection.getCallerClass is not supported. This will impact performance.