(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() < 2 || params.size() > 5)
        throw runtime_error(
            "sendmany \"fromaccount\" {\"address\":amount,...} ( minconf \"comment\" [\"address\",...] )\n"
            "\nSend multiple times. Amounts are double-precision floating point numbers."
            + HelpRequiringPassphrase() + "\n"
            "\nArguments:\n"
            "1. \"fromaccount\"         (string, required) DEPRECATED. The account to send the funds from. Should be \"\" for the default account\n"
            "2. \"amounts\"             (string, required) A json object with addresses and amounts\n"
            "    {\n"
            "      \"address\":amount   (numeric or string) The bitcoin address is the key, the numeric amount (can be string) in " + CURRENCY_UNIT + " is the value\n"
            "      ,...\n"
            "    }\n"
            "3. minconf                 (numeric, optional, default=1) Only use the balance confirmed at least this many times.\n"
            "4. \"comment\"             (string, optional) A comment\n"
            "5. subtractfeefromamount   (string, optional) A json array with addresses.\n"
            "                           The fee will be equally deducted from the amount of each selected address.\n"
            "                           Those recipients will receive less bitcoins than you enter in their corresponding amount field.\n"
            "                           If no addresses are specified here, the sender pays the fee.\n"
            "    [\n"
            "      \"address\"            (string) Subtract fee from this address\n"
            "      ,...\n"
            "    ]\n"
            "\nResult:\n"