(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.
```

const UniValue& input = inputs[idx];
            CBitcoinAddress address(input.get_str());
            if (!address.IsValid())
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, string("Invalid Bitcoin address: ")+input.get_str());
            if (setAddress.count(address))
                throw JSONRPCError(RPC_INVALID_PARAMETER, string("Invalid parameter, duplicated address: ")+input.get_str());
           setAddress.insert(address);
        }
    }
    UniValue results(UniValue::VARR);
    vector<COutput> vecOutputs;
    assert(pwalletMain != NULL);
    LOCK2(cs_main, pwalletMain->cs_wallet);
    pwalletMain->AvailableCoins(vecOutputs, false, NULL, true);
    BOOST_FOREACH(const COutput& out, vecOutputs) {
        if (out.nDepth < nMinDepth || out.nDepth > nMaxDepth)
            continue;
        if (setAddress.size()) {
            CTxDestination address;
            if (!ExtractDestination(out.tx->vout[out.i].scriptPubKey, address))
                continue;
            if (!setAddress.count(address))
                continue;
        }
        CAmount nValue = out.tx->vout[out.i].nValue;
        const CScript& pk = out.tx->vout[out.i].scriptPubKey;
        UniValue entry(UniValue::VOBJ);
        entry.push_back(Pair("txid", out.tx->GetHash().GetHex()));
        entry.push_back(Pair("vout", out.i));
        CTxDestination address;