chore: update lightpush protocol to handle unsupported pubsub topics with clear error codes

[gabrielmer]

Background

The lightpush protocol itself should never be aware of the sharded format of pubsub topics. It is an extension of libp2p's gossipsub.
On a protocol level, the lightpush service node needs to handle requests on unsupported pubsub topics by returning a clear error code.

Acceptance criteria

• Update lightpush protocol to handle unsupported pubsub topics with clear error codes.

[NagyZoltanPeter]

@gabrielmer : I think its clearly part of #2722 WDYT?

[gabrielmer]

@gabrielmer : I think its clearly part of #2722 WDYT?

Oh 100%! Will close it as duplicate! Thank you!