feat: update ENR based on RPC topic subscribe

[SionoiS]

Problem

Subscribing to a new topics via RPC does not update the ENR when using shards.

Suggested solution

discv5 has a way to update the record. Create the same in waku discv5.

Alternatives considered

Restarting the node with new topics always works but is annoying.

Additional context

https://github.com/status-im/nim-eth/blob/285da12bf318a2e21182dc2453a4a30c58f73067/eth/p2p/discoveryv5/protocol.nim#L247

Acceptance criteria

• Subbing to a shard topic like /waku/2/rs/16/0 via RPC should update the ENR in waku discv5.

[SionoiS]

A bit of a conundrum here. Discv5 is no longer in waku_node but rpc handlers call node.subscribe()

It seams like ALL protocols must be in waku_node otherwise we can't access them.

Architecturally, sending information from rpc handlers to whichever protocol needs it in an abstract way (channels?) would be best.

The alternative would be to pass app to the rpc handlers!?

[alrevuelta]

good catch. random idea. perhaps some kind of action can be triggered after subs/unsubs to new topics. like this we can avoid this depencancy. some hook?

[SionoiS]

I talked with @fryorcraken and I guess there's 3 options

1. Don't allow live subscriptions. (remove the API?)
2. Allow but full reset of all connections (shotgun approach!)
3. Design and impl. a smarter system (Is there any benefit?)

The decision will affect peer management.

This seams to be less related to autosharding so I changed the epic.

[SionoiS]

I decided to go with option 4. which is just update the discv5 ENR and don't change anything else.

[SionoiS]

For topic subscriptions we are now using an event system.