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>

freqtrade/templates/base_config.json.j2

@@ -13,6 +13,8 @@
     "fiat_display_currency": "{{ fiat_display_currency }}",{{ ('\n    "timeframe": "' + timeframe + '",') if timeframe else '' }}
     "dry_run": {{ dry_run | lower }},
     "cancel_open_orders_on_exit": false,
+    "trading_mode": "{{ trading_mode }}",
+    "margin_mode": "{{ margin_mode }}",
     "unfilledtimeout": {
         "buy": 10,
         "sell": 10,