feat(backend): add the db connection

backend/database/models/service.py

@@ -0,0 +1,15 @@
+from ..connection import DatabaseConnection
+
+class Service:
+    def __init__(self, service_type_id: int, service_date: str):
+        self.service_type_id = service_type_id
+        self.service_date = service_date
+
+    def save(self, db: DatabaseConnection):
+        query = "INSERT INTO Services (ServiceTypeId, ServiceDate) VALUES (?, ?)"
+        db.execute_query(query, (self.service_type_id, self.service_date))
+
+    @classmethod
+    def get_all(cls, db: DatabaseConnection):
+        query = "SELECT * FROM Services"
+        return db.execute_query_with_return(query)