ALLOWED_HOSTS violations are too loud

Currently, violations of the ALLOWED_HOSTS1 policy trigger an Internal Server Error and raise an exception that is propagated to all logging targets, including admin mail.

That is too loud and unnecessary.

added type::bug label

assigned to @nik

created merge request !731 (merged) to address this issue

mentioned in merge request !731 (merged)

closed with merge request !731 (merged)

mentioned in commit 20bbc901