Standardize API.cs to use JSON Objects (#4868)
Standardize API.cs to use JSON Objects (#4868)

* Standardize API to use JSON Objects

* Address review
jameschch/Lean,jameschch/Lean,QuantConnect/Lean,StefanoRaggi/Lean,jameschch/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,JKarathiya/Lean,AlexCatarino/Lean,QuantConnect/Lean,jameschch/Lean,JKarathiya/Lean,QuantConnect/Lean,AlexCatarino/Lean,AlexCatarino/Lean,StefanoRaggi/Lean,JKarathiya/Lean,QuantConnect/Lean,StefanoRaggi/Lean,StefanoRaggi/Lean,JKarathiya/Lean,jameschch/Lean