Hitbtc3 fetchTradingFee
Hitbtc3 fetchTradingFee

Added fetchTradingFee to hitbtc3 for swap markets:
```
hitbtc3.fetchTradingFee (BTC/USDT:USDT)
2022-03-17T03:25:54.481Z iteration 0 passed in 193 ms

{
  info: { take_rate: '0.0005', make_rate: '0.0002' },
  symbol: 'BTC/USDT:USDT',
  taker: 0.0005,
  maker: 0.0002
}
```

ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt