Supervisory node name can be not unique

During exploratory tests, I noticed that one can change a supervisory node's name to a not unique one, and one doesn't have to use different casing in order to do so.

Reproduction steps:

1. Log into the application as administrator.

2. Go to Administration > Supervisory Nodes.

3. Click the "Edit" button next to any supervisory node.

4. Change the supervisory node's name to a not unique one.

5. Try to update the supervisory node.

6. The supervisory node is updated.

Expected behavior:

• It shouldn't be possible to change the supervisory node's name to a not unique one;

• The changes shouldn't be saved; instead, an error message should be returned.