[FEATURE] Support for Snowflake masking policies and custom classifiers

[anitalySuper]

Snowflake has a custom classifier feature to create classes containing regex that can be used by Snowflake's classification stored procedure to scan for sensitive data in the data warehouse. Combining the results of the classifier with column tagging will then allow us to apply tag-based masking policies to auto detect and mask PII data.

Looking for support for the following:

• custom classifier: https://docs.snowflake.com/en/user-guide/classify-custom-using
• masking policies: https://docs.snowflake.com/en/sql-reference/sql/create-masking-policy
• grants between tags and masking policies (using alter tag): https://docs.snowflake.com/en/sql-reference/sql/alter-tag

[teej]

Added a preview implementation of masking policies in v0.11.0