Scaleset/autoscale cli default min size to zero

[AdamL-Microsoft]

Summary of the Pull Request

> onefuzz scalesets create $NAME --image $IMAGE --region $REGION
# now accepts & implies the following:
> onefuzz scalesets create $NAME --image $IMAGE --region $REGION --min_instances 0

Allows setting the scaleset + autoscale minimum instances count to zero at creation time and also sets zero as the onefuzz scaleset create command default if --min_instances argument isn't specified.

PR Checklist

• Applies to work item: When we create scalesets the minimum number of VM's should be set to zero. #2144
• Passed Integration Tests.

Info on Pull Request

updated:
src/cli/onefuzz/api.py
src/pytypes/onefuzztypes/requests.py

[Porges]

Closes #2144.