db/config.cc: Clarify documentation for `typed_value_ex`
db/config.cc: Clarify documentation for `typed_value_ex`

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