[DOC OCP RHEL] Use Zookeeper or ZooKeeper consistently

It seems the RHEL docs are using both Zoo*K*eeper and Zoo*k*eeper. We should probably unify it. The official name seems to be ZooKeeper with capital K. However, in OCP docs we have many technical fields using Zookeeper which cannot be changed. So we should decide which one we want to use and align at least the places where Zookeeper is just a name reference accordingly.