gitgnore example files

[jcnventura]

Continuing a bit the work in #178, #210 and #245, I'm proposing that the Drupal core-generated example files like default.services.yml, default.settings.php, example.settings.local.php and example.sites.php be excluded from git.

These files are somewhat commonly changed by Drupal core, but I don't see anyone being interested in these changes being tracked in their project repos.

There are some other files added by installing Drupal, but these I concede might be useful to track, in some use cases.
web/.csslintrc
web/.editorconfig
web/.eslintignore
web/.eslintrc
web/.gitattributes
web/.htaccess
web/autoload.php
web/index.php
web/sites/default/services.yml
web/sites/development.services.yml
web/update.php
web/web.config

[webflo]

I think tracking default.services.yml and default.settings.php of is useful. Because you can spot new config options and settings during core update easily. And use add them to your own settings files. Examples are

• $settings['entity_update_batch_size']
• $settings['file_scan_ignore_directories']
• $settings['skip_permissions_hardening']