New config (#6333)

* updated new-config to add trading_mode and margin_mode

* added trading_mode and margin_mode to config examples

* added okex config example

* new file:   config_examples/config_binance_futures.example.json

* removed trading_mode and margin_mode from base_config and binance and okex example

* deleted okex and futures config files

* updated full config file

* updated new-config command to add trading_mode and margin_mode to config

* new file:   config_examples/config_okex_futures.example.json

* removed config_okex_futures.example.json

* added trading_mode to test_start_new_config

* new-config asks exchange before asking futures

* Simplify trading_mode selection

* margin_mode is empty string for spot new configs

* build_config_commands sorted exchanges

* isort

Co-authored-by: Matthias <xmatthias@outlook.com>

config_examples/config_full.example.json

@@ -19,6 +19,8 @@
     "sell_profit_offset": 0.0,
     "ignore_roi_if_buy_signal": false,
     "ignore_buying_expired_candle_after": 300,
+    "trading_mode": "futures",
+    "margin_mode": "isolated",
     "minimal_roi": {
         "40":  0.0,
         "30":  0.01,