feat: Add GQL schema to query total resource slots

[fregataa]

The new GQL schema allows querying the total resource slots of compute sessions. The arguments statuses, project_id, domain_name, resource_group_name, and filter are available.

GQL Query

query TotalResource {
    total_resource_slot(
        domain_name: "default",
    ) {
        occupied_slots
        requested_slots
    }
}

Response

{
    "data": {
        "total_resource_slot": {
            "occupied_slots": "{\"cpu\": \"19\", \"cuda.device\": \"0\", \"mem\": \"7113539584\"}",
            "requested_slots": "{\"cpu\": \"10\", \"cuda.device\": \"0\", \"mem\": \"4093640704\"}"
        }
    }
}

Checklist: (if applicable)

• [x] Milestone metadata specifying the target backport version
• [ ] API server-client counterparts (e.g., manager API -> client SDK)

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📚 Documentation preview 📚: https://sorna--2849.org.readthedocs.build/en/2849/

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📚 Documentation preview 📚: https://sorna-ko--2849.org.readthedocs.build/ko/2849/