feat(coder-labs): add GCP disk snapshot module

[blinkagent]

Summary

This PR adds a new GCP disk snapshot module to the coder-labs namespace that provides disk snapshot functionality for Coder workspaces running on GCP Compute Engine.

Features

• Automatic Snapshots: Creates a disk snapshot when workspaces are stopped
• Single Snapshot: Maintains one snapshot per workspace (overwrites on each stop)
• Restore Option: Users can choose to restore from snapshot or start fresh
• Default to Restore: Automatically selects restore if a snapshot exists
• Pure Terraform: No external CLI dependencies (gcloud not required)
• Workspace Isolation: Snapshots are named and labeled by workspace and owner

How It Works

1. When a workspace stops, a snapshot is created: {owner}-{workspace}-snapshot
2. The snapshot is overwritten each time the workspace stops
3. When starting, users can choose to restore from the snapshot or start fresh
4. If a snapshot exists, restore is selected by default

Usage

module "disk_snapshot" {
  source = "registry.coder.com/coder-labs/gcp-disk-snapshot/coder"

  disk_self_link = google_compute_disk.workspace.self_link
  default_image  = "debian-cloud/debian-12"
  zone           = var.zone
  project        = var.project_id
}

resource "google_compute_disk" "workspace" {
  name = "workspace-${data.coder_workspace.me.id}"
  type = "pd-balanced"
  zone = var.zone
  size = 50

  # Use snapshot if available, otherwise use default image
  snapshot = module.disk_snapshot.snapshot_self_link
  image    = module.disk_snapshot.use_snapshot ? null : module.disk_snapshot.default_image

  lifecycle {
    ignore_changes = [snapshot, image]
  }
}

Requirements

• IAM permissions: compute.snapshots.create, compute.snapshots.delete, compute.snapshots.get
• Or predefined role: roles/compute.storageAdmin

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Created on behalf of @matifali