Validate that a dossier on a `for_individual?` procedure always has
an `individual` associated record.
For this, the individual needs to be built before the record is
validated (i.e. even before the `before_create` callback is run).
This should help with #4596: now if a dossier is created without an
`individual`, or if the `invividual` record is later removed, the
validation will fail.
Currently, a number of dossiers in production are for procedures for
individuals, but don't have a `individual` object.
This is probably because creating the Individual from France Connect
infos fails – but fails quietly, and nullify the relationship.
As a first step, we now raise an exception when the creation from FC
infos fails. We will then identify the issue, and see if we can fix it –
or if we should be resilient to this kind of issues.
