(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.
```

std::vector<uint256> vMerkleBranch; 
        READWRITE(*(CTransaction*)this);
        nVersion = this->nVersion;
        READWRITE(hashBlock);
        READWRITE(vMerkleBranch);
        READWRITE(nIndex);
    }
    int SetMerkleBranch(const CBlock& block);
    /**
     * Return depth of transaction in blockchain:
     * <0  : conflicts with a transaction this deep in the blockchain
     *  0  : in memory pool, waiting to be included in a block
     * >=1 : this many blocks deep in the main chain
     */
    int GetDepthInMainChain(const CBlockIndex* &pindexRet) const;
    int GetDepthInMainChain() const { const CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet); }
    bool IsInMainChain() const { const CBlockIndex *pindexRet; return GetDepthInMainChain(pindexRet) > 0; }
    int GetBlocksToMaturity() const;
    
    bool AcceptToMemoryPool(bool fLimitFree, const CAmount nAbsurdFee);
    bool hashUnset() const { return (hashBlock.IsNull() || hashBlock == ABANDON_HASH); }
    bool isAbandoned() const { return (hashBlock == ABANDON_HASH); }
    void setAbandoned() { hashBlock = ABANDON_HASH; }
};
/** 
 * A transaction with a bunch of additional info that only the owner cares about.
 * It includes any unrecorded transactions needed to link it back to the block chain.
 */
class CWalletTx : public CMerkleTx