Make RandomizedEnv serializable

[Deleted user]

Currently the RandomizedEnv class implements the fluent interface pattern to specify how to randomize the dynamic attributes in a model, however, this breaks the current way we're serializing objects in garage using the Serializable class.
Replace the fluent interface with regular parameters in the constructor of the RandomizedEnv class.
Make sure to update the corresponding test to check the round trip serialization using this function.