Ability for group administrators to customize the “join group” request form

The administrators of our loomio group would like to remove the "Introduce yourself" field from the form that people have to fill in when they request access to the group.
From there the idea came to suggest a feature request to have the possibility to customize this form:

Ability for group administrators to customize the “join group” request form:
- Add/Remove fields
- Define labels for the fields
- Make the fields optional/mandatory