Javascript Functions should default to "cardinality": "many" for EventHubs

The default behavior that we recommend is to batch trigger events. However, we have it as an opt-in setting right now. We should change this so that best practice = default behavior

https://stackoverflow.com/questions/46204764/eventhub-trigger-to-functions-cardinality-with-one-causing-higher-timeouts

Docs on EventHubs settings: https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-event-hubs#trigger---configuration

Start with the Event Hubs trigger configuration documentation and the linked Stack Overflow discussion, then trace where the JavaScript Functions cardinality default is defined. Done means Event Hubs triggers default to cardinality "many" rather than requiring opt-in, with the configuration documentation updated if needed.

Written by the indexing model from the issue text.