BFT Block Puller: A block validator that is updated immediately after a config block is sent to gossip / orderer-pull-buffer

[tock-ibm]

In the peer, the blocks and headers fetched from the orderer are validated using a component in gossip that is validated every time a config block is committed. We need to change that to a mechanism that keeps an earlier view of the config, that is, a config that is updated when a block is given to gossip, rather than committed.

This kind of mechanism already exists in the orderer block puller, and when we unify the two implementation we will create a single instance that behaves in that manner.

[tock-ibm]

Make sure to incorporate https://github.com/hyperledger/fabric/pull/4490 in this PR