workflow: guarantee jump identifiers unicity on new workflows (#74132)

And on existing workflow with no existing identifier duplication.

@@ -1355,0 +1359,4 @@
+                identifier = getattr(item, 'identifier', None)
+                if identifier:
+                    action_ids.append((item, identifier))
+        return action_ids

@@ -2725,0 +2739,4 @@
+        if value == self.identifier:
+            # we don't want to block if a duplication of identifier already exists
+            return False
+        for jump, jump_identifier in self.parent.parent.get_identified_jumps():