Allow searching for user accounts with specific substring in email address

In Hatstall, I want to search for accounts with an email address of a specific domain (`@example.com`) which do not have `Example.com` as their enrollment, to fix their enrollment. Or for account names with `Example` in their name as that is a common way in our project to express that you work for `Example`.

(Reported this under sortinghat and not hatstall as requested by sduenas in internal support ticket 44)