new setting to ignore volumes not annotated

[Acetolyne]

Is your feature request related to a problem? Please describe.
Implementing this in a large environment that has volumes that are not expandable is hard because you have to manually add the annotation to lots of pvc's to ignore the volume
ie: add volume.autoscaler.kubernetes.io/ignore: "false" to all the volumes

Describe the solution you'd like
I propose that there is an environment variable like IGNORE_UNLESS_ANNOTATED that has a default of false so that the current workflow is not changed but that can be set to "true" in which case all volumes are ignored except the ones that have the annotation volume.autoscaler.kubernetes.io/ignore: "false"

Describe alternatives you've considered
manually annotating the hundreds of pvc's across multiple clusters

[Acetolyne]

I have created a PR for this feature if you would like to implement it, always good to have some additional testing
#26

Ill see what I can do about helping out with some of the other feature requests as well when I have some time. Thx for considering this feature.