[Forwardport] Refactored javascript code of admin notification modal popup

[RahulKachhadia]

Original Pull Request

#15341

Description

• Refactored javascript code from popup.phtml according to Magento way.
• Created a JS component file js/system/messages/popup.js

Fixed Issues (if relevant)

1. N/A

Manual testing scenarios

1. N/A

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)

[osrecio]

Hi @rahul-kachhadiya ,

Can you squash your commits in only one? If you have doubts I can assist you via magentocommeng slack.

Thanks!