No longer recommend Zulu Java

[rkoshak]

The Downloads page still recommends and has links to download Zulu Java. That version is no longer the recommended version. We should either remove the recommendation entirely or replace it with a new recommendation.

The Installation docs on the openhab-docs repo should be updated similarly as well so we are consistent.

[Confectrician]

The Installation docs on the openhab-docs repo should be updated similarly as well so we are consistent.

We may have more references over several other docs parts which could be affected.