Method to send all funds / subtracting fees

[Sjors]

I tried to empty my balance, but this is non-trivial because I don't know what the fee is going to be.

phoenix-cli paylnaddress --address="...@phoenixwallet.me"  --amountSat=10000
{
    "paymentHash": "...",
    "reason": "not enough funds in wallet to afford payment"
}

Perhaps an argument like --subtractFee or --all could be added.

[a-nevermind]

+1 on this. A closewallet command where you supply an onchain address would also be cool if a user wanted to shut down a phoenixd instance.