Provide a Function template for TimerTriggered functions

[fgheysels]

We already have templates for Http triggered functions, eventhub triggered functions, etc... I think it would be good to have a template for timer-triggered functions as well.

[stijnmoreels]

💡 Good idea! For isolated functions, we could probably create a middleware component that tracks a triggered timer as a request. Where this and the other built-in functionality (exception handling and correlation) should live... that's another question 😄. We will see once we start developing it, I guess. 👍