Gossipsub further improvements

[sinkingsugar]

The overall picture is ok, obviously likely not bug free but feature wise almost complete.

Few missing things are:

• RPC encodeMessage - currently we threat as optional all empty fields but instead we should take better decisions, also there is this PR that will influence this: gossipsub v1.1: introduce message signing policy libp2p/specs#294
• RPC decodePrune - decode the new gossip 1.1 fields
• Changes introduced by this: gossipsub v1.1: Validation queue protection with Random Early Drop libp2p/specs#292
• Extended validators: https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.1.md#extended-validators

[oskarth]

threat as optional all empty fields but instead we should take better decision

Not sure exactly what this is referring to, but for Waku, having some of that optionality is a feature when it comes to things like metadata protection. Eth2 have slightly different design requirements I believe, so allowing for both would be useful.

EDIT: Looking at https://github.com/ethereum/eth2.0-specs/pull/2060/files I see the StrictNoSign policy seems to overlap with Waku goals.

[dryajov]

Most of this is implemented except the changes introduced in libp2p/specs#292, which is now tracked by #513