databases/py-schemachange: new port

schemachange is a simple python based tool to manage all of your Snowflake
objects. It follows an Imperative-style approach to Database Change Management
(DCM) and was inspired by the Flyway database migration tool. When combined with
a version control system and a CI/CD tool, database changes can be approved and
deployed through a pipeline using modern software delivery practices. As such
schemachange plays a critical role in enabling Database (or Data) DevOps.

PR: 274585
Author: Pat Maddox <pat@patmaddox.com>