Add testing for streamhub events during space deletion

Issue Summary

There should be automated testing of the purge streamhub events that are fired for each page during space deletion to ensure that we delete whiteboards, databases and other custom content types

Created as part of:
https://hello.atlassian.net/wiki/spaces/SRE/pages/3577232943/PIR-18443+-+Sev2+-+Purging+spaces+doesn+t+fire+entity+removed+webhooks

Steps to Reproduce

-

Expected Results

-

Actual Results

-

Workaround

-