Changed defineTasks to return an array...

Instead of the format:
```js
tasks: {
   <taskId>: {
    taskPutUrl: "....."
  },
}
```
We'll now have:
```js
tasks: [
  {
    taskId: "<taskId>",
    taskUrL: '.....',
    taskPutUrl: "....."
  },
]
```

This is eaiser to extend... and easier to consume... the other format is a little backwards... There is really no point in mapping from `taskId` to something... As opposed to do a list. It makes a little sense for artifacts url requests, so we might keep it there...

But I think it should go for this case..

**Note**, I'm currently updating the task-graph scheduler, so I suggest that we hold this back until it's ready for the new format... Which is very close.