* Revert "Revert "APIv2: Replace breakdown module with QueryBuilder (#4283)" (#4292)"

This reverts commit ef5e0e03823dd1a55c990d449966f1ec25484b77.

* Allow querying events and pageviews from sessions table

This is not strictly accurate, especially with shorter time frames, but
is useful for a fallback mechanism. I'll figure out something around
shorter time frames in the future.

See also: https://github.com/plausible/analytics/pull/4292

* Only query events and pageviews in legacy breakdowns