Add config flow to Netgear LTE (#93002)

* Add config flow to Netgear LTE

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* forgot one

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* apply suggestions

* tweak user step

* fix load/unload/dep

* clean up

* fix tests

* test yaml before importing

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* fix startup hanging

* break out yaml import

* fix doc string

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Co-authored-by: Robert Resch <robert@resch.dev>