Peer ID exposure / `WithNoAuthor`

# Summary

Messages currently include the originating peer ID, which may make SP/network identity correlation easier. We should evaluate the privacy benefit of enabling WithNoAuthor against the loss of observability and network-health metrics.

This must be coordinated with other implementation teams, given we are using strict message validate policy https://docs.rs/libp2p-gossipsub/0.49.2/src/libp2p_gossipsub/config.rs.html#42, so all kinds of issues if some nodes allow for unsigned messages and some not. Lotus also uses strict for at
the moment

https://github.com/libp2p/go-libp2p-pubsub/blob/998602bd8c7d1e0a8c721f7b4ca5cb787c12cd7f/pubsub.go#L550

# Additional Links & Resources