[api] Add integration tests using Jest and Supertest

[koistya]

• Update Jest configurations to use projects
• Pre-load environment variables (from env/.local.env file) when running tests (using envars)
• Transpile ESM code to CommonJS since Jest doesn't yet support ESM natively, including a couple of ESM-only Node.js modules such as got
  • Please consider adding native support for ES modules jestjs/jest#4842
  • Meta: Native support for ES Modules jestjs/jest#9430
• Add an integration test example using Jest and Supertest /w inline snapshots
• Add PostgreSQL service to GitHub Actions workflow (here)

Testing GraphQL API field (example)

import request from "supertest";
import { api, db } from "../index";

test(`fetch user(username: "test01")`, async () => {
  const res = await request(api)
    .post("/api")
    .send({
      query: `#graphql
        query {
          user(username: "test01") { id email username }
        }
      `,
    })
    .expect(200)
    .expect("Content-Type", "application/json");

  expect(res.body).toMatchInlineSnapshot(`
    Object {
      "data": Object {
        "user": Object {
          "id": "VXNlcjp0ZXN0MDE=",
          "username": "test01",
          "email": null,
        },
      },
    }
  `);
});