Find handling of Java versions prior Java 8u162

[sdorra]

Issue description

We should find a handling of Java versions prior to Java 8u162, because these version require the Cryptography Extension (JCE) in order to create our GPG private keys. At least we should update our install instructions and perhaps we could create a check on application start.

https://groups.google.com/g/scmmanager/c/pne6pApwids

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[eheimbuch]

Close this since we already atleast Java 11 for SCM-Manager.