Action to select metadata keys that are required

A lot of metadata is sent over at each controller step, but not all this metadata is required.

1. Is it possible to set the scope of metadata returned by the server on the fly (as a controller action).
2. Will this make things faster because less data needs to be sent over, or is this not a speed bottleneck (compared to sending over frame/segmentation tensors etc)?

I could have sworn I saw something about this in an issue/pull request, but I can't find it now. Sorry if this is a duplicate.

------------

For example, if I don't care about the agent, or scene bounds, or specific properties of objects.
```
controller.step(
"UpdateRequiredMetadata",
meta_keys={
'agent': False,
'sceneBounds': False,
'objects':{'axisAlignedBoundingBox': False, 'mass': False}
}
)
```

or if I ONLY care about specific object types?

```
controller.step(
"UpdateRequiredMetadata",
obj_types={
'Painting': False,
'DeskLamp': False,
}
)
```

but later down the line, I change my mind and I do want info about one of them
```
controller.step(
"UpdateRequiredMetadata",
obj_types={
'DeskLamp': True,
}
)
```