Add a GraphQL mutation by placing mutation.cs in the project; it reads books.json, creates a new book from book input, writes JSON, and updates schema to expose the mutation.
Discover how input types pass complex data to GraphQL mutations, define them in code, and use them to create a new book with name, pages, price, publish date, and genre.
Learn to perform a GraphQL mutation with the add book operation, define a book input variable, and return the book id, name, and pages.
