allows for delayed table reflection, column selection and buffer control in sql_database

[rudolfix]

Tell us what you do here

• [x] improving, documenting, or customizing an existing source (please link an issue or describe below)

Relevant issue

Improvements to sql_database

1. reflect tables at runtime - best option for Airflow
2. table adapter callback - ie. to select columns to replicate
3. control buffer sizes in SqlAlchemy