feat(nodeadm): add nodeadm config dump command

[vflaux]

Issue #, if available: #2106

Description of changes:
Add a config dump command to nodeadm that print the resolved config to stdout.
It allow to dump as json (default) or yaml.

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Testing Done
make test: ok

Tested locally with a user-data from an actual instance in a file.
go run cmd/nodeadm/main.go config dump -c file://userdata.txt

[cartermckinnon]

Can you add some more details about what you're trying to accomplish? edit: responded in the linked issue 👍

In general, we want folks to avoid taking a dependency on the nodeadm CLI in their user data, the NodeConfig is intended to be the API surface going forward.