Support device-level configuration across all devices (#1276)
* [WebNN] Only allow free_dimension_override on a device level
* add device_config
* Use Omit to define device config to prevent duplication
* Update custom config instead of checking each property
* Cleanup
* Add back comment
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Co-authored-by: Joshua Lochner <26504141+xenova@users.noreply.github.com>