worker/common/p2p: Use gossipsub to publish commitments

[kostko]

In order to make the system more robust to commitment withholding attacks (see #1804), we should change our libp2p layer to use gossipsub for the publish/subscribe operation. Instead of submitting commitments to specific nodes, they should be broadcast to specific topics.

The topics should likely be something as follows:

• Prefixed by runtime identifier so each runtime has its own set of topics.
• Currently two kinds of topics:
  • TxnSchedulerBatchDispatch, published by txn scheduler nodes, subscribed to by executor nodes; and
  • ExecutorCommit, published by executor nodes, subscribed to by executor nodes and merge nodes.

Peer authorization will need to be changed slightly to allow any committee peer to participate in gossipsub. Topic validators should be configured for the topics to discard any invalid messages (verification should include checking signatures against current committee membership).