Add support for RetryContext

[pragnagopa]

cc @alrod @AnatoliB

Issue: Azure/azure-webjobs-sdk#2595 added support to access retry context within execution context.

This tracking item to expose the same property in python functions. Currently blocked on Azure/azure-functions-host#7048

[vrdmr]

Still needs investigation. :)

[vrdmr]

Fixed by #909