Enhance: spine blocks manifest and spine public keys validation process

[iltoga]

Description

As of now spine block manifests and spine public keys records that are downloaded together with spine blocks are not validated before being pushed, so in theory a misbehaving node could send a correct spine block with a modified version of block manifest and make new nodes download its version of the snapshot referred by it.

Breakdown

• Add general validation of spine block manifest and spine public keys in blockSpineService.ValidateBlock (there is already a TODO for that)

Expected behavior

Before pushing a block, all block attached data (spine block manifests and spine public keys) should be validated against the block's payload hash to make sure they have not been tampered by the sending node

Diagram