stringify cookie value to fix Google Analyitcs Tracking and Cookie Overlay #5596

[bka]

Description

There seems to be a problem in module-cookie/view/frontend/web/js/notices.js. After confirming the cookie restriction dialog, the value "[object Object]" gets saved, which cannot be evaluated anymore in _getAcceptedSaveCookiesWebsites in module-cookie/Helper/Cookie.php

Fixed Issues (if relevant)

1. Google Universal Analytics does not track when Cookie Restriction is enabled  #5596: Google Universal Analytics does not track when Cookie Restriction is enabled
2. Google Analytics Tracking Code cached by Varnish if Cookie Restriction Settings are active #6441: Cookie Restriction Mode Overlay should not be cached by Varnish

Manual testing scenarios

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[vrann]

@bka appreciate your contribution!

[magento-team]

@bka thank you for your contribution