(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.
```

+ HelpExampleRpc("walletpassphrase", "\"my pass phrase\", 60")
        );
    LOCK2(cs_main, pwalletMain->cs_wallet);
    if (fHelp)
        return true;
    if (!pwalletMain->IsCrypted())
        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an unencrypted wallet, but walletpassphrase was called.");
    
    SecureString strWalletPass;
    strWalletPass.reserve(100);
    
    
    strWalletPass = params[0].get_str().c_str();
    if (strWalletPass.length() > 0)
    {
        if (!pwalletMain->Unlock(strWalletPass))
            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "Error: The wallet passphrase entered was incorrect.");
    }
    else
        throw runtime_error(
            "walletpassphrase <passphrase> <timeout>\n"
            "Stores the wallet decryption key in memory for <timeout> seconds.");
    pwalletMain->TopUpKeyPool();
    int64_t nSleepTime = params[1].get_int64();
    LOCK(cs_nWalletUnlockTime);
    nWalletUnlockTime = GetTime() + nSleepTime;
    RPCRunLater("lockwallet", boost::bind(LockWallet, pwalletMain), nSleepTime);
    return NullUniValue;
}
UniValue walletpassphrasechange(const UniValue& params, bool fHelp)