Use generics for triggers

[timtucker-dte]

For Typescript applications that process inputs that with types that are application-specific but consistent, it would make it easier if interfaces for Azure Functions were built with generics.

As an example, defining the types for service bus topics like this:

export type ServiceBusQueueHandler<T = unknown> = (messages: T, context: InvocationContext) => FunctionResult;

export interface ServiceBusQueueFunctionOptions<T = unknown> extends ServiceBusQueueTriggerOptions, Partial<FunctionOptions> {
    handler: ServiceBusQueueHandler<T>;
    trigger?: ServiceBusQueueTrigger;
}

to reflect the type of object that the handler is working with.