Generate schema.graphql from a remote schema using @graphql-codegen/schema-ast

For example, when using graphql-eslint, I need this periodically but always forget how to do it, so here is a note.

Use @graphql-codegen/schema-ast.
The configuration is

codegen.json

{
  "generates": {
    "./graphql/generated/schema.graphql": {
      "schema": "http://localhost:3000/api/graphql",
      "plugins": ["schema-ast"]
    }
  }
}

something like this.