(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 (!ser_action.ForRead())
        {
            mapValue["fromaccount"] = strFromAccount;
            WriteOrderPos(nOrderPos, mapValue);
            if (nTimeSmart)
                mapValue["timesmart"] = strprintf("%u", nTimeSmart);
        }
        READWRITE(*(CMerkleTx*)this);
        std::vector<CMerkleTx> vUnused; 
        READWRITE(vUnused);
        READWRITE(mapValue);
        READWRITE(vOrderForm);
        READWRITE(fTimeReceivedIsTxTime);
        READWRITE(nTimeReceived);
        READWRITE(fFromMe);
        READWRITE(fSpent);
        if (ser_action.ForRead())
        {
            strFromAccount = mapValue["fromaccount"];
            ReadOrderPos(nOrderPos, mapValue);
            nTimeSmart = mapValue.count("timesmart") ? (unsigned int)atoi64(mapValue["timesmart"]) : 0;
        }
        mapValue.erase("fromaccount");
        mapValue.erase("version");
        mapValue.erase("spent");
        mapValue.erase("n");
        mapValue.erase("timesmart");
    }
    
    void MarkDirty()