Add distinct disk for prometheus-tooling vm

[cweibel]

Changes proposed in this pull request:

• Add a new disk configuration to the cloud-config in tooling.
• End goal is to get instance_group prometheus and prometheus-tooling to no longer share disk configurations since they have very different storage space requirements, but doing this in steps since this configuration only exists on prometheus-production
• Part of https://github.com/cloud-gov/private/issues/2594

security considerations

Adds a disk type, no security risks