Create devnet-berkeley.txt in o1-seeds and use it as default devnet bootnode list

Title says it all: in case we don't have Mesa support by the time the devnet hardforks, we can keep running against a Berkeley devnet. 

Next release is going to break devnet-webrtc seed list format anyway as we remove the legacy signaling address parsing... And the "unknown stream protocol id peer rejection" fix makes it effectively a mandatory upgrade, perfect time to include it...