Allow `json_result_force_utf8_encoding` specification in `providers.snowflake.hooks.SnowflakeHook` extra dict

[ttzhou]

Motivation/Justification:

Snowflake's Python connector recommends using json_result_force_utf8_decoding to True, but preserves it as False/no-op for legacy reasons. I've come across cases at work where not setting this returns unexpected results, whereas setting it to True (via a workaround) returns the expected results.

Therefore, I think there is a valid case for allowing this to be passed via connection arguments (via extra).

Relevant 'upstream' Snowflake connector code

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