[ADD] Make bifrost.sh configurable per CHAIN

At the moment , bifrost config file is generated using https://gitlab.com/thorchain/thornode/-/blob/develop/build/scripts/bifrost.sh.

All chains that currently supported is there , it will be added automatically to the config file , thus when bifrost start , it will try to start the chain client , we need to make it configurable based on some environment variables, so we can pick and choose which chain to support

for example, so on testnet , we could disable binance & DOGE chain.