The corresponding FAQ question if the answer was extracted
from a FAQ Document, empty otherwise.
The system's confidence level that this knowledge answer is a
good match for this conversational query. NOTE: The confidence
level for a given <query, answer> pair may change without
notice, as it depends on models that are constantly being
improved. However, it will change less frequently than the
confidence score below, and should be preferred for
referencing the quality of an answer.