fix(docs-infra): include `.gitignore` file in CLI-based docs examples (#38173)

Previously, the `.gitignore` file that is part of the boilerplate files
for CLI-based docs examples (located in
`aio/tools/examples/shared/boilerplate/cli/`) was not added to the
example projects, because it was not included in the boilerplate file
list in `example-boilerplate.js`.

This commit fixes it by adding the `.gitignore` file to the list. This
ensures that docs examples more closely match CLI-generated projects.

PR Close #38173

aio/content/examples/.gitignore

@@ -18,6 +18,7 @@
 **/src/karma.conf.js
 **/.angular-cli.json
 **/.editorconfig
+**/.gitignore
 **/angular.json
 **/tsconfig.json
 **/bs-config.e2e.json

aio/tools/examples/example-boilerplate.js

@@ -16,8 +16,8 @@ const BOILERPLATE_PATHS = {
     '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-puppeteer.conf.js',
-    'e2e/protractor.conf.js', 'e2e/tsconfig.json', '.editorconfig', 'angular.json', 'package.json',
-    'tsconfig.json', 'tslint.json'
+    'e2e/protractor.conf.js', 'e2e/tsconfig.json', '.editorconfig', '.gitignore', 'angular.json',
+    'package.json', 'tsconfig.json', 'tslint.json'
   ],
   systemjs: [
     'src/systemjs-angular-loader.js', 'src/systemjs.config.js', 'src/tsconfig.json',

aio/tools/examples/example-boilerplate.spec.js

@@ -10,7 +10,7 @@ describe('example-boilerplate tool', () => {
     const sharedDir = path.resolve(__dirname, 'shared');
     const sharedNodeModulesDir = path.resolve(sharedDir, 'node_modules');
     const BPFiles = {
-      cli: 20,
+      cli: 21,
       i18n: 3,
       universal: 2,
       systemjs: 7,