Expose all string key/value configs instead of doing it piecemeal.

[pranavsharma]

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Is your feature request related to a problem? Please describe. ORT exposes a bunch of string key/value configs here https://github.com/microsoft/onnxruntime/blob/master/include/onnxruntime/core/session/onnxruntime_session_options_config_keys.h but none of them are exposed by this backend. It would be nice to have them exposed once and for all in a generic fashion as opposed to doing it piecemeal.

Describe the solution you'd like See above.

Describe alternatives you've considered There are none.

Additional context None