Move make_ERD and make_schema_docs to astrodb_utils

This repo does not contain a Python package, but it does contain scripts which require Python packages to run. E.g., `felis`, `eralchemy2`. Should we provide dev instructions for setting up an environment for maintaining the database?

Start by locating the make_ERD and make_schema_docs scripts and checking how they currently depend on felis and eralchemy2. Then determine the intended astrodb_utils location and the repository's existing developer setup documentation; done should include the requested move and clear instructions for maintaining the database environment.

Written by the indexing model from the issue text.