Fixed an issue in Obsidian Registration Entry where group member attribute fields were not being resolved

[Jon-Corey]

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Proposed Changes

This fixes an issue where the Obsidian Registration Entry block was unable to display group member attribute fields. This meant that any group member attribute on a registration was not able to be filled out or edited. Instead of showing the field, the block would show an alert that said "Could not resolve field source 2".

This fixes that issue by adding the group member attribute field source to the list of supported field sources.

Screenshot of before this fix:

Screenshot of after this fix:

Fixes: #5398

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[ethan-sparkdevnetwork]

Thanks @Jon-Corey!