feat: add config module with environment settings and validation

Author: athrael-soju

backend/app/core/config.py

@@ -7,7 +7,6 @@
     BeforeValidator,
     EmailStr,
     HttpUrl,
-    PostgresDsn,
     computed_field,
     model_validator,
 )
@@ -59,7 +58,7 @@ def all_cors_origins(self) -> list[str]:
 
     @computed_field  # type: ignore[prop-decorator]
     @property
-    def SQLALCHEMY_DATABASE_URI(self) -> PostgresDsn:
+    def SQLALCHEMY_DATABASE_URI(self) -> MultiHostUrl:
         return MultiHostUrl.build(
             scheme="postgresql+psycopg",
             username=self.POSTGRES_USER,