feat: Add support for GCE Spot VMs

[mikeb26]

Preflight checklist

• I searched existing issues and did not find a duplicate.
• I checked the README/help text to confirm this is not already supported.

Problem or use case

Currently spotsh supports spot instances on AWS. This is a feature request to add support for working with GCE Spot VMs in an equivalent fasion.

Proposed solution

Introduce primitives under ./gce/ that are equivalent to ./aws/ and wire them into ./cmd/spotsh/main.go

Alternatives considered

No response

Area

launch / EC2 Fleet / Spot placement

Example usage

AWS resource, cost, and security impact

No response

Compatibility considerations

No response

Additional context

https://docs.cloud.google.com/compute/docs/instances/spot