Inform peers that a transaction has been discarded

[AurelienFT]

We want sentries to be able to propagate a discarded transaction of the authority node pool to the API users.

[AurelienFT]

@xgreenx We should have a more homogeneous view of the TxPool across the network with the pending pool etc. Even if this is not implemented do you think we still need it ?

[xgreenx]

I still think we want to do it. Pending pool helps to not discard transactions early, but the block producer still provides a final decision. Block producer already will broadcast information about skipped transactions, but it also would be nice if we will broadcast transactions that were discarded from the TxPool