(from discussion on IRC. Currently a global `settxfee` has to be changed to override the fee rate, it would make sense to be able to specify it on a per-transaction basis. This would continue #7518)

```
-*- jonasschnelli thinks we should probably add a optional feerate parameter to fundrawtransaction
<wumpus> jonasschnelli: there isn't one yet?
-*- jonasschnelli looking..
<wumpus> I'm surprised, would be so much better than changing a global
<jonasschnelli> no.. i don't think so. Maybe there is a PR.
<sipa> there is a pr
<jonasschnelli> Hard to keep track of everything. :)
<wumpus> no, the PR does it wrong
```

Regarding implementation:

```
<jonasschnelli> The ugly thing is, that CreateTransaction uses the static DEFAULT_TARGET
<wumpus> passing in an optional feerate would be the obvious thing to do
<jonasschnelli> So, this would require some refactoring.
<sipa> just add a confirmation target to coincontrol
<jonasschnelli> Yes. This sounds good.
<wumpus> right, just slap it into coincontrol
<sipa> wasn't there a PR that added a bunch of options to fundrawtransaction?
<sipa> including that
<jonasschnelli> Not the feerate.
<jonasschnelli> But the rest is merged.
```

if (fFirst) 
                        {
                            fFirst = false;
                            txout.nValue -= nFeeRet % nSubtractFeeFromAmount;
                        }
                    }
                    if (txout.IsDust(::minRelayTxFee))
                    {
                        if (recipient.fSubtractFeeFromAmount && nFeeRet > 0)
                        {
                            if (txout.nValue < 0)
                                strFailReason = _("The transaction amount is too small to pay the fee");
                            else
                                strFailReason = _("The transaction amount is too small to send after the fee has been deducted");
                        }
                        else
                            strFailReason = _("Transaction amount too small");
                        return false;
                    }
                    txNew.vout.push_back(txout);
                }
                
                set<pair<const CWalletTx*,unsigned int> > setCoins;
                CAmount nValueIn = 0;
                if (!SelectCoins(vAvailableCoins, nValueToSelect, setCoins, nValueIn, coinControl))
                {
                    strFailReason = _("Insufficient funds");
                    return false;
                }
                BOOST_FOREACH(PAIRTYPE(const CWalletTx*, unsigned int) pcoin, setCoins)