Remove unnecessary spacing and margin in the AutomaticFieldEditor

[Yubo-Cao]

• fix: Update the UI for the automatic field editor
• docs: Update CHANGELOG.md

Closes https://github.com/JabRef/jabref-issue-melting-pot/issues/780

Steps to test

1. Open Example Library
2. Select some entries
3. Select Edit > Automatic Field Editor

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• I manually tested my changes in running JabRef (always required)
• [/] I added JUnit tests for changes (if applicable)
• I added screenshots in the PR description (if change is visible to the user)
• I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.

[trag-bot]

@trag-bot didn't find any issues in the code! ✅✨