[BEAM-10870] Add raw private key param to snowflake cross-language python wrapper

[pjotrekk]

• add raw private key param
• small refactor
• fix missing credentials options
• fix table and query set at the same time

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Lang	SDK	Dataflow	Flink	Samza	Spark	Twister2
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Java
Python				---		---
XLang		---		---		---

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Portable	---		---	---	---	---

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[purbanow]

LGTM