Python Schema V2 Templates - Add Trigger function to the Blueprint

[nturinski]

Our tooling expects there to be an assignTo property on the input so that we know where to store the value and where to replace it in the contents later. The Add Trigger function to the blueprint is missing that:

https://github.com/Azure/azure-functions-templates/blob/dev/Functions.Templates/Templates-v2/BlobTrigger-Python/template.json#L133

I only linked the blob trigger, but I suspect that this could be the case for other triggers, so please take a look.