Include Initial ATXs in full in Checkpoint restore

[fasmat]

Description

We need to ensure that Initial ATXs are included with their blobs in a checkpoint. The reason is the Invalid PoST Malfeasance proof proofs requires the original blob to be able to proof the commitment ATX that was used by the identity.

Implementation hints

Alternatively a checkpoint already includes information about the commitmentATX of an identity and a merkle proof for it isn't required any more to consider the malfeasance proof valid. We can just update the validation function of the proof to check if the initial ATX of the identity is golden and then not require the merkle proof to be present/valid.