(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.
```

bool TopUpKeyPool(unsigned int kpSize = 0);
    void ReserveKeyFromKeyPool(int64_t& nIndex, CKeyPool& keypool);
    void KeepKey(int64_t nIndex);
    void ReturnKey(int64_t nIndex);
    bool GetKeyFromPool(CPubKey &key);
    int64_t GetOldestKeyPoolTime();
    void GetAllReserveKeys(std::set<CKeyID>& setAddress) const;
    std::set< std::set<CTxDestination> > GetAddressGroupings();
    std::map<CTxDestination, CAmount> GetAddressBalances();
    std::set<CTxDestination> GetAccountAddresses(const std::string& strAccount) const;
    isminetype IsMine(const CTxIn& txin) const;
    CAmount GetDebit(const CTxIn& txin, const isminefilter& filter) const;
    isminetype IsMine(const CTxOut& txout) const;
    CAmount GetCredit(const CTxOut& txout, const isminefilter& filter) const;
    bool IsChange(const CTxOut& txout) const;
    CAmount GetChange(const CTxOut& txout) const;
    bool IsMine(const CTransaction& tx) const;
    
    bool IsFromMe(const CTransaction& tx) const;
    CAmount GetDebit(const CTransaction& tx, const isminefilter& filter) const;
    CAmount GetCredit(const CTransaction& tx, const isminefilter& filter) const;
    CAmount GetChange(const CTransaction& tx) const;
    void SetBestChain(const CBlockLocator& loc);
    DBErrors LoadWallet(bool& fFirstRunRet);
    DBErrors ZapWalletTx(std::vector<CWalletTx>& vWtx);
    DBErrors ZapSelectTx(std::vector<uint256>& vHashIn, std::vector<uint256>& vHashOut);
    bool SetAddressBook(const CTxDestination& address, const std::string& strName, const std::string& purpose);
    bool DelAddressBook(const CTxDestination& address);
    void UpdatedTransaction(const uint256 &hashTx);
    void Inventory(const uint256 &hash)