Internationalization of Push Rules' Placeholder Text

Currently, these placeholder values are not localized.

Suggestion

Apply the same solution from this MR !18235 (diffs) on the rest of the placeholder texts.

Current	✅New
placeholder: 'Example: @sub\.company\.com$'	placeholder: _('Example: @sub\.company\.com$')

Affected File: ee/app/views/shared/push_rules/_form.html.haml