(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 (mapWallet.count(txin.prevout.hash)) {
                CWalletTx& prevtx = mapWallet[txin.prevout.hash];
                if (prevtx.nIndex == -1 && !prevtx.hashUnset()) {
                    MarkConflicted(prevtx.hashBlock, wtx.GetHash());
                }
            }
        }
    }
    else
    {
        LOCK(cs_wallet);
        
        pair<map<uint256, CWalletTx>::iterator, bool> ret = mapWallet.insert(make_pair(hash, wtxIn));
        CWalletTx& wtx = (*ret.first).second;
        wtx.BindWallet(this);
        bool fInsertedNew = ret.second;
        if (fInsertedNew)
        {
            wtx.nTimeReceived = GetAdjustedTime();
            wtx.nOrderPos = IncOrderPosNext(pwalletdb);
            wtxOrdered.insert(make_pair(wtx.nOrderPos, TxPair(&wtx, (CAccountingEntry*)0)));
            wtx.nTimeSmart = wtx.nTimeReceived;
            if (!wtxIn.hashUnset())
            {
                if (mapBlockIndex.count(wtxIn.hashBlock))
                {
                    int64_t latestNow = wtx.nTimeReceived;
                    int64_t latestEntry = 0;