New attack technique: Read GCE Instance Metadata via the Compute API (gcp.discovery.download-instance-metadata)

[Minosity-VR]

What does this PR do?

New attack technique: gcp.discovery.download-instance-metadata

Motivation

GCP parity with existing AWS attack techniques.

Test results

• stratus detonate gcp.discovery.download-instance-metadata
• compute.instances.get appears in GCP Data Access audit logs (note: this log is very generic and likely not actionable on its own)

Checklist

• The attack technique emulates a single attack step, not a full attack chain
• We have factual evidence & references that the attack technique was used by real malware, pentesters, or attackers
• The attack technique makes no assumption about the state of the environment prior to warming it up

closes #534