[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)

[magento-cicd2]

All committers have signed the CLA.

[VladimirZaets]

Hi, @rahul-kachhadiya , I took your PR into processing, thank you for collaboration.

[magento-engcom-team]

Hi @rahul-kachhadiya. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.3.0 release.