(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.
```

LOCK2(cs_main, pwalletMain->cs_wallet);
    UniValue obj(UniValue::VOBJ);
    obj.push_back(Pair("walletversion", pwalletMain->GetVersion()));
    obj.push_back(Pair("balance",       ValueFromAmount(pwalletMain->GetBalance())));
    obj.push_back(Pair("unconfirmed_balance", ValueFromAmount(pwalletMain->GetUnconfirmedBalance())));
    obj.push_back(Pair("immature_balance",    ValueFromAmount(pwalletMain->GetImmatureBalance())));
    obj.push_back(Pair("txcount",       (int)pwalletMain->mapWallet.size()));
    obj.push_back(Pair("keypoololdest", pwalletMain->GetOldestKeyPoolTime()));
    obj.push_back(Pair("keypoolsize",   (int)pwalletMain->GetKeyPoolSize()));
    if (pwalletMain->IsCrypted())
        obj.push_back(Pair("unlocked_until", nWalletUnlockTime));
    obj.push_back(Pair("paytxfee",      ValueFromAmount(payTxFee.GetFeePerK())));
    return obj;
}
UniValue resendwallettransactions(const UniValue& params, bool fHelp)
{
    if (!EnsureWalletIsAvailable(fHelp))
        return NullUniValue;
    if (fHelp || params.size() != 0)
        throw runtime_error(
            "resendwallettransactions\n"
            "Immediately re-broadcast unconfirmed wallet transactions to all peers.\n"
            "Intended only for testing; the wallet code periodically re-broadcasts\n"
            "automatically.\n"
            "Returns array of transaction ids that were re-broadcast.\n"
            );
    LOCK2(cs_main, pwalletMain->cs_wallet);
    std::vector<uint256> txids = pwalletMain->ResendWalletTransactionsBefore(GetTime());
    UniValue result(UniValue::VARR);
    BOOST_FOREACH(const uint256& txid, txids)