Cannot create new role on project page without a valid regen address

[Cory]

Describe the bug
Currently there's a uniqueness constraint on regen address. Since there is already one "role" with a blank regen address (empty string value) in the database table, all role creations without a valid regen address are failing.

The solution is to change the uniqueness constraint to allow for multiple records with null addresses.

This was previously thought to be a duplicate of #2282, but when investigating with @blushi last week, we discovered that it was actually a separate bug.

To Reproduce

Expected behavior

Screenshots

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Additional context

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For Admin Use

• Not duplicate issue
• Appropriate labels and zenhub epics applied
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