IsTransient returns true if the error returned by the LaunchDarkly API is either unexpected, or unable to be resolved by the user.

LaunchDarkly API uses the X-Ratelimit-Reset header to communicate when to retry after a 429 Fallback to default backoff if header can't be parsed https://apidocs.launchdarkly.com/#section/Overview/Rate-limiting Method is curried in order to avoid stubbing the time package and fallback Backoff in unit tests.