Update AlphaStreamsBrokerageModel.cs
Update AlphaStreamsBrokerageModel.cs

Implement explicity method for getting security leverage. Adjusted leverage based on available research regarding hedge funds and PBs.

jameschch/Lean,AlexCatarino/Lean,AlexCatarino/Lean,JKarathiya/Lean,AlexCatarino/Lean,StefanoRaggi/Lean,QuantConnect/Lean,jameschch/Lean,QuantConnect/Lean,QuantConnect/Lean,jameschch/Lean,JKarathiya/Lean,JKarathiya/Lean,StefanoRaggi/Lean,StefanoRaggi/Lean,jameschch/Lean,JKarathiya/Lean,StefanoRaggi/Lean,QuantConnect/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,jameschch/Lean