feat: add studentCost route

src/libs/convert/studentCost.js

src/libs/middlewares/aggregateData.js

src/libs/middlewares/id2str.js

src/libs/middlewares/studentRevenueParser.js

src/libs/routes_v1/api.js

src/libs/routes_v1/studentCost.js

src/libs/routes_v1/studentRevenue.js