(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 (nBytes >= MAX_STANDARD_TX_SIZE)
                {
                    strFailReason = _("Transaction too large");
                    return false;
                }
                dPriority = wtxNew.ComputePriority(dPriority, nBytes);
                
                if (fSendFreeTransactions && nBytes <= MAX_FREE_TRANSACTION_CREATE_SIZE)
                {
                    
                    double dPriorityNeeded = mempool.estimateSmartPriority(nTxConfirmTarget);
                    
                    if (dPriority >= dPriorityNeeded && AllowFree(dPriority))
                        break;
                }
                CAmount nFeeNeeded = GetMinimumFee(nBytes, nTxConfirmTarget, mempool);
                if (coinControl && nFeeNeeded > 0 && coinControl->nMinimumTotalFee > nFeeNeeded) {
                    nFeeNeeded = coinControl->nMinimumTotalFee;
                }
                if (coinControl && coinControl->nFeeRate > CFeeRate(0))
                    nFeeNeeded = coinControl->nFeeRate.GetFee(nBytes);
                
                
                if (nFeeNeeded < ::minRelayTxFee.GetFee(nBytes))
                {
                    strFailReason = _("Transaction too large for fee policy");
                    return false;
                }
                if (nFeeRet >= nFeeNeeded)