Add support for gpu (device) attestation policy

[bpradipt]

With recent support for multiple device attestation (specifically gpu) in Trustee, the policy configuration must be exposed via Trustee operator.
This is the issue to track the work.

[bpradipt]

cc @cclaudio @lmilleri

[Jakob-Naucke]

Good to know: Since confidential-containers/trustee#900, trustee-operator effectively requires users of trustee:main to set default_cpu.rego and default_gpu.rego.
When setting just default_cpu.rego, Trustee will attempt to write a default GPU policy, but to the read-only file system attached by trustee-operator.

apiVersion: v1
kind: ConfigMap
metadata:
  name: attestation-policy
  namespace: operators
data:
  default_cpu.rego:
    package policy
---
apiVersion: confidentialcontainers.org/v1alpha1
kind: KbsConfig
metadata:
...
spec:
...
  kbsAttestationPolicyConfigMapName: attestation-policy

leads to

/* policy_file_path is "/opt/confidential-containers/attestation-service/policies/opa/default_cpu.rego" */
[2025-09-16T13:45:36Z WARN  attestation_service::policy_engine::opa] Policy default_cpu already exists, so the default policy will not be written.
/* now policy_file_path is "/opt/confidential-containers/attestation-service/policies/opa/default_gpu.rego" */
Error: Attestation error: Failed to initialize attestation service

Caused by:
    0: Failed to initialize attestation service
    1: Failed to write attestation service policy to file: Read-only file system (os error 30)
    2: Read-only file system (os error 30)

Let me know if this should be branched out to a bug report, but it isn't an issue for the currently shipped v0.13.0 yet.

[lmilleri]

@Jakob-Naucke which path are you using for the policy (in the trustee config map)? The recommended one is /opt/confidential-containers/attestation-service/policies . But yes, it seems a problem for the next release of the operator

[Jakob-Naucke]

This was reproduced from the blog, so it was that directory.