Add v5.3.0 changes to CHANGELOG.md

[vitaliyboykocontributor]

Included Mage-os support and multiple fixes such as a workaround for the "thread context was already set" exception, a typo in NewObserverDialog form, and deprecation of ActionUpdateThread.OLD_EDT on DumbAwareActions. These updates provide critical fixes and new features to enhance the plugin's functionality.

Description (*)

Fixed Issues (if relevant)

1. Fixes magento/magento2-phpstorm-plugin#<issue_number>

Questions or comments

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 integration/functional tests (if applicable)
• All automated tests passed successfully (all builds are green)