p2p suggestions: save bootstrap file

[shyba]

I have some suggestions for the p2p code, so instead of just describing them I decided to open a PR to show what I mean. Feel free to adapt parts of it as/if it feels right.

• Save and restore top 100 connected peers as a bootstrap file to aid on restarts. This may later be used on the reconnect function to reboostrap in case of a connection loss. I often see this feature across p2p clients.

EDIT: removed other changes that were solved with peer info manager and the last qol

This PR now only adds support for a bootstrap file (should help bringing connectivity to a new node from an existing one or during reboots, but wont change anything on already good ones)