(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.
```

CAmount nAmount = AmountFromValue(params[2]);
    if (nAmount <= 0)
        throw JSONRPCError(RPC_TYPE_ERROR, "Invalid amount for send");
    if (params.size() > 3)
        
        (void)params[3].get_int();
    string strComment;
    if (params.size() > 4)
        strComment = params[4].get_str();
    CWalletDB walletdb(pwalletMain->strWalletFile);
    if (!walletdb.TxnBegin())
        throw JSONRPCError(RPC_DATABASE_ERROR, "database error");
    int64_t nNow = GetAdjustedTime();
    
    CAccountingEntry debit;
    debit.nOrderPos = pwalletMain->IncOrderPosNext(&walletdb);
    debit.strAccount = strFrom;
    debit.nCreditDebit = -nAmount;
    debit.nTime = nNow;
    debit.strOtherAccount = strTo;
    debit.strComment = strComment;
    pwalletMain->AddAccountingEntry(debit, walletdb);
    
    CAccountingEntry credit;
    credit.nOrderPos = pwalletMain->IncOrderPosNext(&walletdb);
    credit.strAccount = strTo;
    credit.nCreditDebit = nAmount;
    credit.nTime = nNow;
    credit.strOtherAccount = strFrom;
    credit.strComment = strComment;