Add ability not to declare env variables in script

[alexander-shustanov]

All env variables should be available via extension fields on env object.

It is needed to support nested objects in env variables.

For nested objects special classes should be generated.

Example:

env:

{
    "local": {
        "ordersApi": {
            "token": "...",
            "port": 8080
        }
    },
    "prod": {
        "ordersApi": {
            "token": "..."
        }
    }
}

implicit declare in script

val env.ordersApi: OrdersApiEnv

synthetic class:

class OrdersApiEnv {
    val token: String
    val port: Integer? // as port only exists in prod env
}