Add saved queries for ongoing Snowflake threats

[egibs]

Background

Snowflake has released additional information on investigating and identifying malicious behavior to Snowflake accounts: https://community.snowflake.com/s/article/Communication-ID-0108977-Additional-Information

This PR adds saved queries to identify malicious behavior.

These queries require that Panther's read-only role has access to the snowflake.account_usage audit database (this may need to be done by the Snowflake admins).

Changes

• Adds Snowflake queries applicable to the aforementioned KB article

Testing

• New tests pass as expected