Enable creation of custom fields

[simonaszilinskas]

Description

The current registration form customization is limited to selecting additional fields from a predefined list. To offer more flexibility to organizations, we should allow administrators to create custom fields directly from the back office, enabling them to add unique fields that are not available in the predefined selection.

Proposed Solution:

1. Develop a user interface in the back office for creating custom fields.
2. Modify the registration form configuration to include custom fields alongside the predefined fields.
3. Update the form rendering and data storage mechanisms to handle custom fields seamlessly.

Quick illustration of how it might look like: