Issue Summary

When making calls to "/rest/api/user/search?query=", the query value can only find forward substrings.
For example, if the user has an email "example@test.org", the search "query=exam" will return the user, however the search "query=xample@test.org" will not return the user.

As a consequence, searching for users by email such as "query=@test.org" will no longer return users as it used to.

Steps to Reproduce

1. Use the endpoint to search for existing users by email domain.

Expected Results

The users with the substring are found

Actual Results

The expected users are not returned.

Workaround

Currently, the best workaround is to use the endpoint /rest/api/3/users/search to page through all users, then use the "self" attributes that are returned to get the details of each user. Finally, filter the results as desired.