bug(nodeadm): run validation in config check

[ndbaker1]

Issue #, if available:

mentioned in #2123

Description of changes:

The nodeadm config check command validates the document can be parsed, but if it is incorrectly formatted or missing data then fields are left empty and the command still reports the config is valid.

This PR adds the same validation call to the parsed NodeConfig in config check and in the init command.

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Testing Done

cat << EOF > test.yaml
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="//"

--//
Content-Type: application/node.eks.aws

---
APIVersion: node.eks.aws/v1alpha1
Kind: NodeConfig

--//--
EOF

# before
> go run ./cmd/nodeadm/main.go config check -c file://../test.yaml
{"level":"info","ts":1738745826.997185,"caller":"config/check.go:27","msg":"Checking configuration","source":"file://../test.yaml"}
{"level":"info","ts":1738745826.9985948,"caller":"config/check.go:36","msg":"Configuration is valid"}

# after
> go run ./cmd/nodeadm/main.go config check -c file://../test.yaml
{"level":"info","ts":1738745868.4194193,"caller":"config/check.go:28","msg":"Checking configuration","source":"file://../test.yaml"}
{"level":"fatal","ts":1738745868.420988,"caller":"nodeadm/main.go:36","msg":"Command failed","error":"Name is missing in cluster configuration","stacktrace":"main.main\n\t/home/nbakerd/workspace/ami/nodeadm/cmd/nodeadm/main.go:36\nruntime.main\n\t/home/nbakerd/go/pkg/mod/golang.org/[email protected]/src/runtime/proc.go:272"}

See this guide for recommended testing for PRs. Some tests may not apply. Completing tests and providing additional validation steps are not required, but it is recommended and may reduce review time and time to merge.

[cartermckinnon]

Thanks @ndbaker1!