Documentation: specify if ParameterWith<type>Validators is intended for external usage

At the moment the documentation contains multiple types for the `function` package with names such as `ParameterWithValidators`. These types are also (of course) public. These types contain member fields for `Parameter` type inputs and slices of `ParameterValidator`. At the moment these types all appear to mostly facilitate "get" return functionality for the module, and not really support inputs. However, the definition signatures would appear to be interesting if they could be externally consumed.

Could the Go package documentation for the `ParameterWithValidators` please be updated to specify if these are for module internal usage, or whether they are external facing?