feat: Autosharding protocol changes for req-resp protocols

[chair28980]

This tracks work necessary to change req-resp protocol requirements for pubsub topic fields to be optional in wire specifications. This implies a spec change, changes to clients to use the simplified specs and changes to server-side Waku implementations to interpret client requests with no populated pubsub topics correctly.

Priority: Not critical for launch (all main benefits of autosharding is already achieved via API changes)

[fryorcraken]

Suggested to drop this from E:1.2: Autosharding for autoscaling. Internal discussion in progress

[fryorcraken]

Iceboxing this as it's a cleanup/nice to have that does not have strong added value.

May be done if it allows to simplify code/logic to enable work in the area.