Search SSO API endpoint with email instead of username

• For https://gitlab.e.foundation/e/infra/backlog/-/issues/3395

• The result for an API call to https://accounts.eeo.one/auth/admin/realms/eeo.one/users?exact=true&username=totptester3 immediately after creation is []

• The result for an API call to https://accounts.eeo.one/auth/admin/realms/eeo.one/users?exact=true&email=totptester3@murenatest.io immediately after creation is [{"username": "totptester3", "id":"...",...}]

• The code of keycloak doesn't change all the way to latest version, so this fix should apply to new versions of keycloak too