Add HTTP retry mechanism

[JordanSussman]

Use case:

If an error is returned by the client (connection errors, etc.), or if a 500-range response code is received, then a retry is invoked after a wait period.

Thoughts:

Looks like the standard golang HTTP library doesn't have a native way to support this. It may be worthwhile to explore other libraries like heimdall or go-retryablehttp that support this.