Pebblo 0.1.18 snowflake v2

[Raj725]

Made the following updates to an Original PR(on top of lint fixes and rebase with the master):

• Removed unused methods
• Use pop instead of get to remove the extra fields from the metadata
• Dropped page_content modification and recommended use of page_content_columns while loading data
  Example:

  SnowflakeLoader(
     query=QUERY,
     user=SNOWFLAKE_USER,
     password=SNOWFLAKE_PASS,
     account=SNOWFLAKE_ACCOUNT,
     warehouse=SNOWFLAKE_WAREHOUSE,
     role=SNOWFLAKE_ROLE,
     database=SNOWFLAKE_DATABASE,
     schema=SNOWFLAKE_SCHEMA,
     page_content_columns=["ADDITIONAL_COMMENTS", "OPEN_ENDED_QUESTIONS"],
     metadata_columns=['AUTH_INFO', 'METADATA_SOURCE']
  ),