add source to blob_trigger

[YunchuWang]

Fixes #197

Context and Problem: Issue #197 highlighted a discrepancy in the Azure Functions documentation and the actual behavior of the BlobTrigger binding. According to the documentation, the BlobTrigger binding supports a source argument that allows setting the source of the triggering event to EventGrid for lower latency. However, in practice, the BlobTrigger binding does not currently accept this argument, and the default method for detecting changes in a blob container is through the standard polling mechanism (LogsAndContainerScan).

Objective: This Pull Request aims to align the functionality of the BlobTrigger with the documented features by introducing the EventGrid source option. This will enable users to leverage Event Grid-based triggers for blob storage, providing a more efficient and lower-latency mechanism for blob event handling.