(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 (!EnsureWalletIsAvailable(fHelp))
        return NullUniValue;
    if (fHelp || params.size() > 1)
        throw runtime_error(
            "keypoolrefill ( newsize )\n"
            "\nFills the keypool."
            + HelpRequiringPassphrase() + "\n"
            "\nArguments\n"
            "1. newsize     (numeric, optional, default=100) The new keypool size\n"
            "\nExamples:\n"
            + HelpExampleCli("keypoolrefill", "")
            + HelpExampleRpc("keypoolrefill", "")
        );
    LOCK2(cs_main, pwalletMain->cs_wallet);
    
    unsigned int kpSize = 0;
    if (params.size() > 0) {
        if (params[0].get_int() < 0)
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, expected valid size.");
        kpSize = (unsigned int)params[0].get_int();
    }
    EnsureWalletIsUnlocked();
    pwalletMain->TopUpKeyPool(kpSize);
    if (pwalletMain->GetKeyPoolSize() < kpSize)
        throw JSONRPCError(RPC_WALLET_ERROR, "Error refreshing keypool.");
    return NullUniValue;
}
static void LockWallet(CWallet* pWallet)