Error starting Eclair on testnet4 (cannot retrieve feerates) #3105
Description
Eclair calls into bitcoin core to estimate onchain fees, which almost always fails on testnet4 because blocks are empty. Setting fallbackfee in bitcoin.conf does not help (it provides default values for methods like sendtoaddress but not estimatesmartfee which still fails).
A simple solution would be to add such a fallbackfee setting to elair.conf, valid only on test networks, that eclair would fallback to if bitcoin core's fee estimation fails.