(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.
```

"\nExamples:\n"
            "\nThe total amount in the wallet\n"
            + HelpExampleCli("getbalance", "") +
            "\nThe total amount in the wallet at least 5 blocks confirmed\n"
            + HelpExampleCli("getbalance", "\"*\" 6") +
            "\nAs a json rpc call\n"
            + HelpExampleRpc("getbalance", "\"*\", 6")
        );
    LOCK2(cs_main, pwalletMain->cs_wallet);
    if (params.size() == 0)
        return  ValueFromAmount(pwalletMain->GetBalance());
    int nMinDepth = 1;
    if (params.size() > 1)
        nMinDepth = params[1].get_int();
    isminefilter filter = ISMINE_SPENDABLE;
    if(params.size() > 2)
        if(params[2].get_bool())
            filter = filter | ISMINE_WATCH_ONLY;
    if (params[0].get_str() == "*") {
        
        
        
        CAmount nBalance = 0;
        for (map<uint256, CWalletTx>::iterator it = pwalletMain->mapWallet.begin(); it != pwalletMain->mapWallet.end(); ++it)
        {
            const CWalletTx& wtx = (*it).second;
            if (!CheckFinalTx(wtx) || wtx.GetBlocksToMaturity() > 0 || wtx.GetDepthInMainChain() < 0)
                continue;
            CAmount allFee;
            string strSentAccount;