cql3: add generating base key from index keys
cql3: add generating base key from index keys

A function that computes base partition/clustering key from index view
primary key is provided.

scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla