Support blob trigger with event grid

[ejizba]

There's a "source" property that you set to "EventGrid" for a blob trigger, which we don't support yet.

More details here, and also we need to update these docs once it's working:
https://learn.microsoft.com/en-us/azure/azure-functions/functions-event-grid-blob-trigger?tabs=isolated-process&pivots=programming-language-javascript#update-the-function-to-use-events