Reduce confusion for "magic" binding expressions

[ejizba]

We've had several people get confused by these (example 1, 2, 3). I think the main problem is that these are hard-coded string values that basically perform magic under the covers and the documentation is hard-to-find. Would be nice if we could add some Intellisense or helper methods to make it easier to understand.

Example binding expression:

const blobOutput = output.storageBlob({
  connection: "AzureWebJobsStorage",
  path: "helloworld/{DateTime:MM-dd-yyyy H:mm:ss}.json",
});

Example route parameter:

app.http('httpTrigger1', {
    methods: ['GET', 'POST'],
    authLevel: 'anonymous',
    route: 'httpTrigger1/{id}',
    handler: httpTrigger1
});

[Sarabadu]

I think it would be also good to note in docs that is not posible to set any of those values on runtime, you can only use binding parameters declared in the input, or binding expressions.