Dear Mautic Community,
This bundle enables you to extend Custom Field groups by just modifying one file in the plugin:
< GitHub - mzagmajster/mautic-field-group-bundle: Add/edit field groups in Mautic via config params >
In the future I plan to enable adding field groups via Mautic GUI, as well as some other things, so stay tuned 
I suggest you always use master branch when deploying in production enviornment.
Hope someone finds it, useful.