Added Optional Foreign HKs for Snowflake

[JPLangner]

Added opportunity to create Non Historized Links on Snowflake without any foreign Hashkeys, as it might be the case that a Non Historized Link exists on its own.

[tkirschke]

Hi @JPLangner and thanks for reaching out!

I understand the need to make this optional! I have reviewed and tested your code and it works as it should!

But before merging these changes, I have two more requests:

• Bring these changes on code level also to BigQuery and Exasol
• Adapt the Wiki to point out, that foreign_hashkeys is now optional

Once these two things are done, I will test again and if it all works, then merge the PR!

Best regards
Tim

[tkirschke]

Hi @JPLangner , sorry for the late reply here, I saw that you added the optionality for BigQuery and Exasol, thanks!
If you now also add it for Redshift and Postgres, I would merge it!