feat: add gcp get vm instance component

[WashingtonKK]

Summary

Adds a new Compute • Get VM Instance action to the GCP integration. It fetches the current state of a Compute Engine VM and emits its details on the default output channel.

What it does

• Accepts a VM instance via the dropdown (zone-encoded path) or an expression chained from an upstream node (e.g. selfLink from gcp.createVM)
• Resolves zone and name via the existing parseInstancePath helper (relative paths and full selfLink URLs both work)
• Rejects cross-project selfLinks — the integration's bound project is authoritative
• Fails loudly if the instance is not found, so stale expressions don't silently pass
• Emits: instanceId, name, selfLink, status, zone, machineType, internalIP, externalIP

Use cases

• Status checks — gate downstream steps on a VM being RUNNING
• Detail lookup — surface IPs or machine type for later workflow nodes
• Health gates — branch a workflow based on instance state

Demo Video

[superplanehq-integration]

👋 Commands for maintainers:

• /sp start - Start an ephemeral machine (takes ~30s)
• /sp stop - Stop a running machine (auto-executed on pr close)

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