Add DB migration tool

[afred]

Because

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I can use a migration tool to

Tasks

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1. create / set up Chowda db for tests
2. create / set up Chowda db for local development
3. use of SQLModel.metadata.create_all(engine) is removed

In order to

• have a single tool for creating / setting up database in test, development, and production environments
• have a production-ready tool for managing DB schema changes without data loss or wholesale DB reset operations
• avoid concurrency issues in Github CI due to using SQLModel.metadata.create_all()

  ERROR tests/test_app.py - sqlalchemy.exc.IntegrityError: (psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint "pg_type_typname_nsp_index"
  DETAIL:  Key (typname, typnamespace)=(mediatype, 2200) already exists.
  

Done when

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Additional context

Most sources say that Alembic is the best tool for SQLAlchemy, and thus also SQLModel.

• SQLModel PR for adding Alembic Migration docs and tutorials
• Tutorial from Alembic official docs

[afred]

closed by #73