fix(gocardless): Ignore refund not found when not comming from lago

[vincent-pochet]

Context

Some PaymentProviders::Gocardless::HandleEventJob jobs are raising BaseService::NotFoundFailure with a gocardless_refund_not_found error message.

It seems to happen when the related refund is not found in Lago database.
By looking at the event payload, it appears that no metadata was attached to the event, meaning that the refund was not emitted from Lago.

Since we cannot handle this event, we should ignore them and not raise any error.

Description

This PR uses an approach that was previously introduce to handle stripe webhooks:

• Check for the Refund into the DB
• If not found, check for the metadata in the payload
• raise an error only if the metadata matches a Lago resource (invoice), return a success result otherwise