Add query cache hit information to Percona Response time distribution plugin (MDEV-4568)

Include two new columns to QUERY_RESPONSE_TIME:
query_cache_count => number of queries returned from query cache
query_cache_total => query cache response time

the non query cache queries could be found as:
SELECT
time,
count,
total,
query_cache_count,
query_cache_total,
(count-query_cache_count) AS non_query_cache_count,
(total-query_cache_total) AS non_query_cache_total
FROM QUERY_RESPONSE_TIME