[ENH] - Convert to using factory modules in lieu of a factory method in the DAG file

[jerdra]

A meeting decision was made to shift over the scope of DAGs from specific sub-tasks to full end-to-end study DAGs. To deal with compartmentalizing sub-tasks for testability/code readability we decided on having a bunch of factory modules which construct and return an airflow TaskGroup

https://www.astronomer.io/guides/task-groups

The current datasource DAG needs to be re-written as a factory module so that a taskgroup is returned. The DAG module should only be responsible for chaining task groups.