API - Stats_v2 doesn't show projects without events

### Problem Statement

Currently the endpoint
https://(org).sentry.io/api/0/organizations/(org)/stats_v2/?category=replay&field=sum%28quantity%29&groupBy=outcome&groupBy=project&interval=4h&project=-1&statsPeriod=30d
only shows the projects that actually have events connected with it, but it would make sense to also show projects when they have a zero event count.

This helps in extracting the volume through API's to be used in other tools like splunk

API [Docs](https://docs.sentry.io/api/organizations/retrieve-event-counts-for-an-organization-v2/)

### Solution Brainstorm

_No response_

### Product Area

Unknown

┆Issue is synchronized with this [Jira Improvement](https://getsentry.atlassian.net/browse/FEEDBACK-1903) by [Unito](https://www.unito.io)