Convert QRT to use new MySQL 8 histogram

In PS 8 we retired support for QRT plugin:

https://www.percona.com/doc/percona-server/8.0/changed_in_version.html#features-removed-from-percona-server-version

We need to modify the Query Response Time plugin dashboard to consume histogram information.

1. How is Histogram enabled in PERFORMANCE_SCHEMA - is it on by default?
2. Should Histogram be disabled based on any criteria? # of tables or something else?