Reconsider RetryPolicy errors for non-retriable responses

[chlowell]

RetryPolicy currently returns an error when it receives a non-retriable, non-2xx response:

azure-sdk-for-rust/sdk/typespec/typespec_client_core/src/http/policies/retry/mod.rs

Lines 168 to 181 in 65ef3f7

	if !RETRY_STATUSES.contains(&status) {
	debug!(
	"server returned error status which will not be retried: {}",
	status
	);
	// Server didn't return a status we retry on so return early
	let error = Error::full(
	error_kind,
	http_error,
	format!(
	"server returned error status which will not be retried: {status}"
	),
	);
	return Err(error);

In the abstract, this is strange because the policy's responsibility is to obtain a non-retriable response, retrying requests as necessary according to its configuration. Interpreting those responses is the caller's responsibility. Concretely, this behavior creates practical difficulties for callers who expect such a response (e.g., a client may elicit an authentication challenge) or want to handle it with a different error type.