(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.
```

#include <assert.h>
#include <boost/algorithm/string/replace.hpp>
#include <boost/filesystem.hpp>
#include <boost/thread.hpp>
using namespace std;
CWallet* pwalletMain = NULL;
CFeeRate payTxFee(DEFAULT_TRANSACTION_FEE);
unsigned int nTxConfirmTarget = DEFAULT_TX_CONFIRM_TARGET;
bool bSpendZeroConfChange = DEFAULT_SPEND_ZEROCONF_CHANGE;
bool fSendFreeTransactions = DEFAULT_SEND_FREE_TRANSACTIONS;
const char * DEFAULT_WALLET_DAT = "wallet.dat";
/**
 * Fees smaller than this (in satoshi) are considered zero fee (for transaction creation)
 * Override with -mintxfee
 */
CFeeRate CWallet::minTxFee = CFeeRate(DEFAULT_TRANSACTION_MINFEE);
/**
 * If fee estimation does not have enough data to provide estimates, use this fee instead.
 * Has no effect if not using fee estimation
 * Override with -fallbackfee
 */
CFeeRate CWallet::fallbackFee = CFeeRate(DEFAULT_FALLBACK_FEE);
const uint256 CMerkleTx::ABANDON_HASH(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
/** @defgroup mapWallet
 *
 * @{
 */
struct CompareValueOnly
{
    bool operator()(const pair<CAmount, pair<const CWalletTx*, unsigned int> >& t1,