BE warnings: setup database schema & alembic

• create a database schema
• create a first alembic migration
• include admin script to automatically run alembic
• create a pydantic SQLmodel type for the warnings database
• verify that a warnings table (and database) exist where you can see the column names and correct types
• information for the schema: https://docs.google.com/presentation/d/1PL3X6AjDFPSvmHh4rarMBMoEF2KFfLHIMs9yPeXeepE/edit#slide=id.g25f85a2a964_0_43