AAI-119 don't automatically update the production DB - use migrations

[marius-mather]

Description

AAI-119: because we were using SQLModel.create_all() to automatically set up the DB tables, we couldn't run migrations (tables would already exist). Stop automatically creating tables so we can use alembic to manage the DB - requires more manual work, but means we have more control over the DB and won't accidentally alter data with an update

Changes

• Only run create_all() when we're using a sqlite database, like we do in dev
• Add the migration for the status approval enum
• Add documentation for how to manually run the migrations on the production server

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)

How to Test Manually (if necessary)

N/A

[amandazhuyilan]

Just nick picking again on docs...