fix: make containerd config check compatible with new config version

[shvbsle]

Issue #, if available:
The containerd config check test fails since it assumes that we will always find pause image by the name sandbox_image but in newer config versions this does not hold true.

• In containerd config version = 2 expect to find pattern sandbox_image = "registry.k8s.io/pause:3.10.1"
• In containerd config version = 3 expect to find pattern sandbox = 'registry.k8s.io/pause:3.10.1'

For more details: https://github.com/containerd/containerd/blob/main/docs/cri/config.md

Description of changes:
Attempt to extract 'sandbox' from the config to be compatible with latest containerd config.

Testing

go test -v -tags=e2e ./test/cases/nvidia/... -timeout=0 -args \                        
    --test.timeout=30m \
    --test.v \
    --test.run=TestContainerdConfig/containerd-config-check \
    -efaEnabled=true \
    -nvidiaTestImage=${REPO}.dkr.ecr.us-west-2.amazonaws.com/shvbsle/${IMAGE_TAG}
2025/11/20 21:17:14 No node type specified. Using the node type p6e-gb300.36xlarge in the node groups.
=== RUN   TestContainerdConfig
=== RUN   TestContainerdConfig/containerd-config-check
2025/11/20 21:17:14 [Setup] Applying containerd-check DaemonSet manifest.
=== RUN   TestContainerdConfig/containerd-config-check/DaemonSet_becomes_ready
2025/11/20 21:17:14 [Assess] Waiting up to 1 minute for containerd-check DS to become Ready...
2025/11/20 21:17:19 [Assess] containerd-check DS is Ready.
=== NAME  TestContainerdConfig/containerd-config-check
    containerd_test.go:61: [Teardown] Removing containerd-check DS (no additional logs).
    containerd_test.go:65: [Teardown] containerd-check DS removed successfully.
--- PASS: TestContainerdConfig (5.06s)
    --- PASS: TestContainerdConfig/containerd-config-check (5.06s)
        --- PASS: TestContainerdConfig/containerd-config-check/DaemonSet_becomes_ready (5.02s)
PASS
ok      github.com/aws/aws-k8s-tester/test/cases/nvidia 22.074s

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[wwvela]

LGTM

[shvbsle]

CI failing due to no space left on runner device. Will retry in a while. Should not be related to our changes

[mselim00]

the neuron build CI should pass if rebased on main btw #719

[mselim00]

lgtm.

an aside, this could be better as a python script or if there were some hypothetical command-line tq that handles toml serialization

[shvbsle]

flaky build ci due to space running out. Trying it once agian