query_processor: add CQL logging to all major execute call sites.
query_processor: add CQL logging to all major execute call sites.

Add missing CQL query logging to statement prepare, internal execute,
batch execute.
The logging is done under log level "trace".

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