feat: remove GraphQL service empty resource requirement; add option to change playground endpoint

[crookse]

Closes #646

TODO

• Update documentation
  • PR: feat(drash/v2.x): improved graphql docs website-v2#170
  • Page: https://drash-land-git-feat-graphql-improved-docs-drash-land.vercel.app/drash/v2.x/tutorials/services/drash-approved-services/graphql

Summary

• refactor: GraphQLService creates the GraphQL playground resource at startup time
• feat: add option playground_path to allow user to define different GraphQL playground endpoint
• test: updates GraphQLService test

Example Usage

// app.ts

import { Drash, GraphQL, GraphQLService } from "./deps.ts";

// Set up your GraphQL environment

const schema = GraphQL.buildSchema(`
  type Query {
    greeting: String
  }
`);

const root = {
  greeting: () => { // or greeting: (source, args, context, info) => {
    return "Hello world!";
  },
};

// Instantiate the GraphQL service

const graphQl = new GraphQLService({
  schema,
  graphiql: true,
  rootValue: root,
});

const server = new Drash.Server({
  hostname: "localhost",
  port: 1447,
  protocol: "http",
  resources: [],
  services: [graphQl],
});

server.run();

console.log(`Server running at ${server.address}.`);