Example YAML configuration and Example DAG instantiation DAGs

[oscarrezab]

Add example configuration and instantiation for S3ToSnowflakeDag and SFTPToSnowflakeDag.

[sleblanc23]

Thanks for this Oscar! There are a few optional things I'd like to remove to make these a bit shorter. Could you please take out start_date and slack_conn_id from both YAML configurations, and also shorten the second config blocks to just two years/tenants for each DAG type? For example, remove 2020 and 2021 from the S3 DAG and lone_star and wiggins from the SFTP DAG.

[sleblanc23]

Thanks, Oscar!