Add the exception_ptr of the unhandled exception to retry_context

[rahuldutta90]

Context: This will give a better handling of exceptions especially winhttp errors (https://docs.microsoft.com/en-us/windows/win32/winhttp/error-messages) from clients overriding the azure::storage::Retry_policy. Currently our service is overriding your retry_policy. This gives us more flexibility to handle retries on append scenarios.

1) Added exception_ptr to retry_context 2) Pass the exception other than storage_exception to retry_context in excecutor.

[Jinming-Hu]

/AzurePipelines run Azure.azure-storage-cpp

[azure-pipelines[bot]]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[Jinming-Hu]

/AzurePipelines run Azure.azure-storage-cpp

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[Jinming-Hu]

Unit test looks good

[rahuldutta90]

@katmsft I see tests failing. I checked out master and there also see these test failing. Shouldnt be related to my changes right?

[Jinming-Hu]

@rahuldutta90 Don't worry. That's the problem of test cases.