[TC-221]: init template-backend-service (#1)

https://eva.avroid.tech/desk/cards?obj=Task:TC-221

Начальная версия сервиса-шаблона

Co-authored-by: Nadezhda <nadezhda.lavrentieva@avroid.team>
Reviewed-on: https://git.avroid.tech/Templates/template-backend-service/pulls/1
Reviewed-by: Victor Stratov <victor.stratov@avroid.tech>

src/database/postgresql.py

@@ -0,0 +1,17 @@
+from sqlalchemy import MetaData, create_engine
+from sqlalchemy.orm import Session, declarative_base, sessionmaker
+
+from src.settings import WebAppSettings
+
+
+class PGConnector:
+    def __init__(self, settings: WebAppSettings) -> None:
+        self.pg_engine = create_engine(
+            f"postgresql://{settings.postgres_user}:{settings.postgres_password}@{settings.postgres_host}:"
+            f"{settings.postgres_port}/{settings.postgres_db}",
+        )
+        self.pg_session = sessionmaker(self.pg_engine, class_=Session)
+
+
+PGBase = declarative_base()
+pg_metadata = MetaData()