User created constraints have a default joint name of "UserConstraint" that cannot be edited

Constraints created by users are all given the same Joint Name of "UserConstraint" and it cannot be edited. This makes referencing these joints individually impossible.

Regression?: No
This occurs in 4.20

1. Create a new project with the Third Person Template
2. Open the Mannequin's Physics Asset
3. Find the constraint under the Head bone called "head: neck_01 Constraint"
4. Note that it has a Joint Name of "head" and delete the constraint
5. Right-click on the physics body for neck_01 (the circular icon with 3 green dots) and create a new constraint by hovering over "Constraints" and select Head in the list
6. Click on the new constraint that was created under Head to replace the one that was deleted
   Result: The "Joint Name" in the details panel is "UserConstraint" and cannot be edited
   Expected: The "Joint Name" in the details panel either has a unique name or can be edited