Expose API to set visibilitytimeout and TTL for individual queue messages

#### Investigative information

Timestamp: 08-03-2019 17:30Z
Function App version (1.0 or 2.0): 2.0.12332.0
Function App name: rixwscrape
Function name(s) (as appropriate): enqueue
Invocation ID:
Region: UK South

#### Repro steps

The Queue Storage output binding allows the configuration of a global or per function visibilityTimeout for _retries_ of failed messages, but no means of setting this programatically for the initial visibilityTimeout per message. All that can be specified is the message body.

#### Expected behavior

To be specify a queue item as an object, rather than a plain string. Something like:

`context.bindings.myQueueItem = [
{ message: "message 1", visibilityTimeout: 30, messageTimeToLive: 3600 },
{ message: "message 2", visibilityTimeout: 60, messageTimeToLive: 3600 },
];`

#### Actual behavior

Not supported

#### Known workarounds

I can achieve what I need to do by using the @azure/storage-queue SDK:
[https://docs.microsoft.com/en-us/javascript/api/%40azure/storage-queue/messagesurl?view=azure-node-preview#enqueue-aborter--string--messagesenqueueoptionalparams-](https://docs.microsoft.com/en-us/javascript/api/%40azure/storage-queue/messagesurl?view=azure-node-preview#enqueue-aborter--string--messagesenqueueoptionalparams-)

`messagesUrl.enqueue(Aborter.none, JSON.stringify(result, undefined, 2), {
visibilitytimeout: 30,
messageTimeToLive: 3600
}),`

But it would be way more developer-friendly if these options could be specified via an output binding - I've got c 20 quite verbose LOC at the moment which could be 2-3.

Start with the Queue Storage output binding and its context.bindings.myQueueItem contract, then compare the requested per-message fields with the @azure/storage-queue MessagesUrl.enqueue options described in the issue. Done means queue output messages can specify individual visibilityTimeout and messageTimeToLive values, while existing plain-string output continues to work and the behavior is covered by the relevant binding tests.

Written by the indexing model from the issue text.