(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 (mapArgs.count("-mintxfee"))
    {
        CAmount n = 0;
        if (ParseMoney(mapArgs["-mintxfee"], n) && n > 0)
            CWallet::minTxFee = CFeeRate(n);
        else
            return InitError(AmountErrMsg("mintxfee", mapArgs["-mintxfee"]));
    }
    if (mapArgs.count("-fallbackfee"))
    {
        CAmount nFeePerK = 0;
        if (!ParseMoney(mapArgs["-fallbackfee"], nFeePerK))
            return InitError(strprintf(_("Invalid amount for -fallbackfee=<amount>: '%s'"), mapArgs["-fallbackfee"]));
        if (nFeePerK > HIGH_TX_FEE_PER_KB)
            InitWarning(_("-fallbackfee is set very high! This is the transaction fee you may pay when fee estimates are not available."));
        CWallet::fallbackFee = CFeeRate(nFeePerK);
    }
    if (mapArgs.count("-paytxfee"))
    {
        CAmount nFeePerK = 0;
        if (!ParseMoney(mapArgs["-paytxfee"], nFeePerK))