feat: C bindings for Waku Relay

[Ivansete-status]

Problem

nwaku can't be easily exported to other environments, such as NodeJS or Rust.

Suggested solution

Have nwaku C bindings so that a NodeJS user can easily start a Waku node in Relay mode.

Additional context

This is a first step of having a full operative Waku node in other platforms. For now we focus on the Waku Relay protocol.
We want to tackle the nwaku C-bindings option of: "use nwaku with NodeJS" - #1332
The final goal that we chase: "C-bindings for Kotlin, Rust, etc" - #904

Acceptance criteria

• Have dynamic library (waku.so) for unix systems.
• Have a static library (waku.a) for unix systems.
• Have a C program that links nwaku libraries. That program should operate as a Relay node, allowing:
  • subscribe/unsubscribe from a PubSub topic.
  • send a message to a PubSub topic.
• Have a npm package so that a "Waku Relay" node can be started from NodeJS.
• Waku relay example in Python.
• Waku relay example in Golang.