Preflight checks failing to load for lots of invalid emails

Issue Summary

Confluence Server instances that have many invalid users (~ 1000) may experience a very long loading time with the spinner continuously spinning and then (in google chrome) the browser tab crashing

Steps to Reproduce

This can be reproduced for Confluence Server instances with very large sets of invalid emails when viewing the Check For Errors page.

Expected Results

User validation preflight checks successfully load and display correctly

Actual Results

User validation preflight checks may take a long time to load and potentially crash (or force refresh for IE) the browser tab.

Workaround

Current workaround is to disable the user validation preflight checks using the following dark feature flags

migration-assistant.disable.invalid-emails-check
migration-assistant.disable.duplicate-emails-check