Add example demonstrating Filecoin-compatible gossipsub usage

[seetadev]

Create a py-libp2p example aligned with Filecoin pubsub parameters

Document mesh parameters and message validation expectations
Outcome: Reference example for Filecoin-style pubsub

Outcome: Reference example for Filecoin-style pubsub

[imApoorva36]

Hey @seetadev , I plan to work on this, will be sharing a detailed implementation plan as well soon

[seetadev]

@imApoorva36 : great, please do