[REQ][typescript-inversify] Change 'optional' behavior

Created by: siada

Is your feature request related to a problem? Please describe.

When generating models for a .net API, I have to add the [Required] attribute to every model property to avoid the typescript-inversify generator creating view model properties as optional.

The problem with them being optional is typescripts 'undefined by default' approach - you end up with a lot of undefined checks against properties that are never going to be undefined.

The problem this causes is the model validator on the .net side is validating properties as [Required] that are actually allowed to be null - but they're defined as [Required] so typescript-inversify doesn't try to make them undefined

Describe the solution you'd like

Change the default behaviour of declaring a typescript-inversify model property from:

name?: string

to a union type:

name: string | null