Add call_activity_with_retry to DurableOrchestrationContext class

[Nick Holt]

💡 Feature description
The DurableOrchestrationContext class has both a call_activity_with_retry method and a call_sub_orchestrator_with_retry method. Often times the call_http method fails for unknown and external reasons. Adding a call_http method that includes an option to retry a specified number of times would go a long way to improve the reliability of durable orchestrations. Adding an exponential backoff would be a nice plus.

💭 Describe alternatives you've considered
The obvious alternative is to wrap your API call into an activity function and use the call_activity_with_retry method. Creating new activity functions for each API call tends to bloat projects though. The v2 programming model may address this concern though - I'm still stuck on the v1 programming model for now.