Persistent PeerId

[NiKrause]

• using the KeyStore's privateKey for the PeerId
• do not save the keyPair inside the config

Fixes: #77

[NiKrause]

I was thinking about the question of whether Voyager should have a persistent PeerId or not. From a security perspective, it might be wanted or good to have a temporary PeerId for, for example, every restart of the node.

From the perspective of a browser that wants to pin files, it is necessary to have a fix PeerId. Otherwise, the browser would have no idea, who's the Voyager is in the network.

On the other hand, Voyager could publish via Gossibsub that there's an OrbitDB Pinning Service around. But wait, isn't that already communicated via identify? Is it possible to find and connect quickly to certain peers who speak a certain protocol without pubsub or bootstrap nodes?