Generate python exceptions for conjure errors

[tgsiegel]

When using conjure generated clients, any error is represented by a generic ConjureHTTPException that requires manual parsing to determine exactly what the error is. If I have some conjure error

SomeException:
  docs: Something went wrong
  code: INVALID_ARGUMENT
  namespace: MyService
  safe-args:
    argument: string
    object: SomeObjectWithFields
  unsafe-args:
    unsafeArgument: string 

I would like to get some generated python exception

class SomeException(Exception):
    """
    Something went wrong
    """

    NAMESPACE = "MyService"
    ERROR_CODE = "INVALID_ARGUMENT" # probably want this to be an enum
    ERROR_NAME = "MyService:SomeException"

    def __init__(self, conjure_exception: ConjureHTTPError):
        # do some validation
        self.unsafe_args = ...
        self.safe_args = ...

    @staticmethod
    def is_instance(self, conjure_exception: ConjureHTTPError) -> bool:
        # check if the conjure exception is this
        return conjure_exception.error_name == SomeException.ERROR_NAME

That way I can use this in my code to convert a ConjureHTTPError into a more user friendly exception, with some actual types

try:
    return some_service.endpoint()
except ConjureHTTPError as err:
    if SomeException.is_error(err):
        actual_exception = SomeException(err)
        raise UserFriendlyError(actual_exception.safe_args.argument, actual_exception.object.some_object_field)
	# maybe check some other exceptions here too
    raise err

Both java and typescript conjure clients do this, I think it would be really useful to have it in python as well