Dynamic position size

[carkod]

This can be baked into streaming.position_updates():

• we'd need to enable a new bot.field for dynamic position sizing based on base_order. e.g. like a percentage
• Then position_update checks this value and if it's set, then we'd place order according to this percentage. Sort of
  • 10 USDT + dynamic_position_size = 10% = 1 USDT place order quantity
  • check if there's available balance
  • then carry out place order if there is.

This will also unlock rebalancing strategies which are very good against range/sideway market regimes.