[Task]: Add a migration to duplicate the customs scanner rules for webhook

[willdurand]

Description

In order to be able to switch customs to webhook, we need to duplicate the existing scanner rules. That'll make the migration easier so let's write a migration script for that (customs doesn't have new rules very often so it's fine to do that at any point in time)

Acceptance Criteria

see above

┆Issue is synchronized with this Jira Task

[willdurand]

For QA: once this lands, there should be new scanner rules for webhook, the same as the customs ones, but disabled.