PoC: Replace string templating with SQLAlchemy

[scriptdruid]

just a poc to test usage of sqlachemy as required by use case

• able to read a timestamp from snowflake table
• needs mocking to local as next step , supported as seen in docs

[scriptdruid]

Not for mergeing, please discard, only for meetup and idea

[scriptdruid]

next steps

• Implement ORM for the same code , start with timestamp
• Add local mocking
• Udpate hub.py to incorporate sql alchemy replacements

[michael-the1]

@vipulrai91 @hellowithchicken Thanks again for your efforts during the spring last Saturday! To summarize the sprint:

• We set up a Snowflake account and learned the basics of Data Vault.
• The overarching goal is to replace the use of string templates with SQLAlchemy. Hopefully this will pave the way forward to supporting backends other than Snowflake (e.g. BigQuery, postgres).
• To that end, it would be nice if this PR can demonstrate a small example where hub_link_dml.py is expressed in terms of SQLAlchemy objects. Since this file consists of a select statement and a merge statement, I think it should be a simple select statement and to use those results in a MergeInto object.
  • For this minimal example, we don't need to worry about supporting other dialects yet so using MergeInto is totally fine.

Hope those guidelines will help you out and once again thank you for your contribution!