tests: add checking computed columns in SI
tests: add checking computed columns in SI

The test case checks if token column generated for global indexing
is indeed only present in global indexes and is marked as a computed
column.

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