java-driven fixes

Merged Alexander Sosedkin requested to merge java-fixes into master

LEGACY: bump 1023 key size to 1024: Last year Tomas Mraz said this is done for historical reasons and can be changed now: https://bugzilla.redhat.com/show_bug.cgi?id=1882178#c2

policygenerators/java: add javasystem backend: turns out jdk.tls.ephemeralDHKeySize is not a java security property and has to live in a different file to have an effect https://bugzilla.redhat.com/show_bug.cgi?id=1883312

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