Change "vsam init" page into "caching service init"

[1000TurquoisePogs]

"zwe init vsam" is not needed in a default configuration of zowe v3, because the caching-service uses infinispan by default.
vsam is still allowed, but is deprecated and not recommended as it is just inferior and more trouble.

since the purpose of the vsam page is about setup of storage for the caching service, this page could be changed to focus on general caching service setup, such as covering infinispan configuration if infinispan is chosen, or vsam setup of vsam is chosen.