alternator-test: add scan case for key equality filtering
alternator-test: add scan case for key equality filtering

With key equality filtering enabled, a test case for scanning is provided.

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