Understand possible DiskType.validDiskSize formats

[mziccard]

DiskType.validDiskSize is documented as:

An optional textual description of the valid disk size, such as "10GB-10TB".

We should understand the format this field can have so that we can split it into two numbers (e.g. minSize and maxSize).

[danoscarmike]

This has been added to our feature backlog: https://github.com/GoogleCloudPlatform/google-cloud-java/wiki/Feature-backlog. This issue will be closed but is linked in the backlog and can continue to be used for comment and discussion.