Introducing engines in package.json

[LunaticMuch]

This PR introduces engines in package.json

I see a value in having engines, particularly for avoiding possible issues with node <16 (still commonly found in many systems) that have different SSL options.

With a node <16 you can easily get into this issue because of old SSL providers, which in turns requires to enable " export NODE_OPTIONS=--openssl-legacy-provider" (cf --openssl-legacy-provider)

Command failed: npm run build
    warn  - No ESLint configuration detected. Run next lint to begin setup
    Browserslist: caniuse-lite is outdated. Please run:
    npx browserslist@latest --update-db

    Why you should do it regularly:
    https://github.com/browserslist/browserslist#browsers-data-updating
    node:internal/crypto/hash:71
      this[kHandle] = new _Hash(algorithm, xofLen);
                      ^

    Error: error:0308010C:digital envelope routines::unsupported

      30 |         process.chdir(cwd)
      31 |         execSync('npm install')
    > 32 |         execSync('npm run build')
         |         ^
      33 |       })
      34 |
      35 |       afterEach(() => {

      at BulkUpdateDecorator.hashFactory (__tests__/__fixtures__/custom-output-directory/node_modules/next/dist/compiled/webpack/bundle5.js:133863:18)
      at BulkUpdateDecorator.update (__tests__/__fixtures__/custom-output-directory/node_modules/next/dist/compiled/webpack/bundle5.js:133764:50)
      at __tests__/__fixtures__/custom-output-directory/node_modules/next/dist/compiled/webpack/bundle5.js:56911:9
      at process.processImmediate (__tests__/__fixtures__/custom-output-directory/node:internal/timers:447:9) {
        opensslErrorStack: [ 'error:03000086:digital envelope routines::initialization error' ],
        library: 'digital envelope routines',
        reason: 'unsupported',
        code: 'ERR_OSSL_EVP_UNSUPPORTED'
      }
      at Object.execSync (__tests__/index.js:32:9)

[votemike]

How does this affect pnpm?