Fix for #15041 Adding a new fieldset to the admin category editor changes the position of the 'General' fieldset

[vasilii-b]

Description

When a custom fieldset is added to the admin category editor, the General section (the one with "Enable category", "Include in Menu" and "Category Name") moves to the last position of the form.
Full description in #15041

Fixed Issues (if relevant)

1. Adding a new fieldset to the admin category editor changes the position of the 'General' fieldset. #15041
   

Manual testing scenarios

Provided in #15041

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-engcom-team]

Hi @vasilii-b. Thank you for your contribution
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[magento-engcom-team]

Hi @VladimirZaets, thank you for the review.
ENGCOM-2758 has been created to process this Pull Request

[magento-engcom-team]

Hi @vasilii-b. Thank you for your contribution.
We will aim to release these changes as part of 2.2.7.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.