Checkout current docs setup from scylla-4.x branch

Brings several changes that are in scylla-4.x as of commit
c85f7b9
Subpages should be added to documentation tree correctly now.

Author: Bouncheck

docs/_utils/javadoc.sh

@@ -14,4 +14,4 @@ fi
 mvn javadoc:javadoc -T 1C
 [ -d $OUTPUT_DIR ] && rm -r $OUTPUT_DIR
 mkdir -p "$OUTPUT_DIR"
-mv -f core/target/site/apidocs/* $OUTPUT_DIR
+mv -f driver-core/target/site/apidocs/* $OUTPUT_DIR