Suggestion: Make models compatable with System.Text.Json deserialization

[douglasg14b]

Title pretty much states it!

I know you don't have much time for this project, this issue is mostly just to track this.

Working with System.Text.Json for model de-serialization is valuable in cases where this SDK is used only for it's models, for data that's already at hand or stored locally, and where the desire to use Newtonsoft is low.