Add unconnected database support

Also adds a helper for doing nested config parsing since we're getting
more and more

src/infra/db.py

@@ -0,0 +1,15 @@
+from sqlalchemy.orm import DeclarativeBase
+from src.config.database import Database as DatabaseConfig
+from sqlalchemy import create_engine
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def get_database(config: DatabaseConfig):
+    engine = create_engine(config.url, echo=config.echo)
+    # Ensure that all tables exist in the database
+    Base.metadata.create_all(engine)
+
+    return engine