chore: migrate Relay logic fron app.nim to waku_node.nim

[gabrielmer]

Background

Currently there's logic related to a Waku Node's configuration at the application level (app.nim). This shouldn't happen there in the first place, and as a consequence, there's important node configuration logic not available when we try to directly create a node.

Because of this, we have lots of duplicated code in libwaku that should belong to the Waku Node's core logic.

Acceptance criteria

A Waku Node's Relay and RLN-Relay's configuration logic should be decoupled from app.nim and belong to waku_node.nim