Implement EIP-1459 for basic node discovery

[oskarth]

Problem

Currently there's no node discovery for Waku, but we instead use hardcoded static nodes.

Solution

The most basic form of node discovery, as was previously investigated, is likely https://eips.ethereum.org/EIPS/eip-1459

See https://rfc.vac.dev/spec/6/#node-discovery and https://vac.dev/dns-based-discovery

Additionally, corresponding update in Waku v2 recommending the use of DNS based discovery (identical to Waku v1)

As a further enhancement, we can look into using Discovery v5 module like Nimbus, but this isn't initially needed.

cc @jm-clius fyi on practical next steps re discovery once we think this is a priority

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UPDATE 2021-06-14:

Subtasks:

• DNS-based Discovery: Create raw specification vacp2p/rfc#398: Create raw specification
• DNS-based Discovery: DNS Resolver #615: DNS Resolver
• DNS-based Discovery: Merkle tree implementation #616: Merkle tree
• DNS-based Discovery: Client implementation #617: Client implementation