Timeout fee estimation request

[dpad85]

Getting the fees estimation is needed to properly reestablish channels. The wallet needs to offer a valid fee to its peer.

To do that we ask the electrum server for a fee estimation (see Peer.updateEstimateFee). However this request does not currently timeout. So if the electrum server we connect to is failing to respond, the node is stuck forever. It also does not respond to its LN peer, and eventually the connection is dropped by the peer.

We should instead timeout the request and disconnect from Electrum. We could then publish some kind of failure event so that the end client can display an error or connect to another electrum server.

We could also fallback to a known fee provider such as mempool.space, bitgo, ..., but that may not make a lot of sense, since we will eventually need to connect to a working electrum server anyway.

[t-bast]

This changes drastically once we have #649, and I believe won't be an issue anymore. Closing for now and we'll re-open after #649 if something needs to be done.