APIv2: Replace breakdown module with QueryBuilder (#4293)

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

This reverts commit ef5e0e0.

* 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: #4292

* Only query events and pageviews in legacy breakdowns

CHANGELOG.md

@@ -16,6 +16,7 @@ All notable changes to this project will be documented in this file.
 - Increase hourly request limit for API keys in CE from 600 to 1000000 (practically removing the limit) plausible/analytics#4200
 - Make TCP connections try IPv6 first with IPv4 fallback in CE plausible/analytics#4245
 - `is` and `is not` filters in dashboard no longer support wildcards. Use contains/does not contain filter instead.
+- `bounce_rate` metric now returns 0 instead of null for event:page breakdown when page has never been entry page.
 
 ### Fixed
 

lib/plausible/stats/base.ex

@@ -250,6 +250,8 @@ defmodule Plausible.Stats.Base do
   end
 
   defp select_session_metric(:percentage, _query), do: %{}
+  defp select_session_metric(:conversion_rate, _query), do: %{}
+  defp select_session_metric(:group_conversion_rate, _query), do: %{}
 
   def filter_converted_sessions(db_query, site, query) do
     if Query.has_event_filters?(query) do