Feature: support p2p reconnections

Is your feature request related to a problem? Please describe. https://github.com/romanz/electrs/issues/531#issuecomment-945502410

For P2P connections to bitcoind, it would be important that there is no timeout at all. It can take hours, or even days, to get a free P2P slot to a given bitcoind node. Or, your connection could be dropped by bitcoind for whatever reason, then you'll need to retry to connect again.

Describe the solution you'd like We should probably try to reconnect a few times / for short period of time before failing electrs.

Describe alternatives you've considered Currently, we just fail on the first p2p connection error: https://github.com/romanz/electrs/issues/531