build(docs-infra): use puppeteer to get a browser for docs examples tests (#35381)

In #35049, integration and AIO tests were changed to use the browser
provided by `puppeteer` in tests. This commit switches the docs examples
tests to use the same setup.

IMPLEMENTATION NOTE:
The examples are used to create ZIP archives that docs users can
download to experiment with. Since we want the downloaded projects to
resemble an `@angular/cli` generated project, we do not want to affect
the project's Protractor configuration in order to use `puppeteer`.

To achieve this, a second Protractor configuration is created (which is
ignored when creating the ZIP archives) that extends the original one
and passes the approperiate arguments to use the browser provided by
`puppeteer`. This new configuration (`protractor-puppeteer.conf.js`) is
used when running the docs examples tests (on CI or locally during
development).

PR Close #35381

aio/tools/examples/example-boilerplate.js

@@ -15,8 +15,9 @@ const BOILERPLATE_PATHS = {
     'src/environments/environment.prod.ts', 'src/environments/environment.ts',
     'src/assets/.gitkeep', 'browserslist', 'src/favicon.ico', 'karma.conf.js',
     'src/polyfills.ts', 'src/test.ts', 'tsconfig.app.json', 'tsconfig.spec.json',
-    'tslint.json', 'e2e/src/app.po.ts', 'e2e/protractor.conf.js', 'e2e/tsconfig.json',
-    '.editorconfig', 'angular.json', 'package.json', 'tsconfig.json', 'tslint.json'
+    'tslint.json', 'e2e/src/app.po.ts', 'e2e/protractor-puppeteer.conf.js',
+    'e2e/protractor.conf.js', 'e2e/tsconfig.json', '.editorconfig', 'angular.json', 'package.json',
+    'tsconfig.json', 'tslint.json'
   ],
   systemjs: [
     'src/systemjs-angular-loader.js', 'src/systemjs.config.js', 'src/tsconfig.json',