Hashicorp Plugin: enable key version caching by default

It is necessary to enable key version caching in the default configuration, because with the current default settings, many users believe that caching is not really there or do not understand the difference between caching version numbers and key values and why enabling caching for key values does not significantly reduce the number of requests to server (because almost every key reading is preceded by a request for its version and this still results in a request to the Hashicorp Vault server).