[netdata] add otNetDataReplacePublishedExternalRoute() API (#9013)

This commit adds a public OT API to replace a previously published
external route entry in the Thread Network Data. It also adds a
related CLI command, and updates `test_netdata_publisher` to
validate the new behavior.

tests/scripts/thread-cert/node.py

@@ -2380,6 +2380,10 @@ class NodeImpl:
         self.send_command(f'netdata publish route {prefix} {flags} {prf}')
         self._expect_done()
 
+    def netdata_publish_replace(self, old_prefix, prefix, flags='s', prf='med'):
+        self.send_command(f'netdata publish replace {old_prefix} {prefix} {flags} {prf}')
+        self._expect_done()
+
     def netdata_unpublish_prefix(self, prefix):
         self.send_command(f'netdata unpublish {prefix}')
         self._expect_done()

tests/scripts/thread-cert/test_netdata_publisher.py

@@ -461,6 +461,19 @@ class NetDataPublisher(thread_cert.TestCase):
         routes = leader.get_routes()
         self.check_num_of_routes(routes, num - 1, 0, 1)
 
+        # Replace the published route on leader with '::/0'.
+        leader.netdata_publish_replace(EXTERNAL_ROUTE, '::/0', EXTERNAL_FLAGS, 'med')
+        self.simulator.go(0.2)
+        routes = leader.get_routes()
+        self.assertEqual([route.split(' ')[0] == '::/0' for route in routes].count(True), 1)
+        self.check_num_of_routes(routes, num - 1, 1, 0)
+
+        # Replace it back to the original route.
+        leader.netdata_publish_replace('::/0', EXTERNAL_ROUTE, EXTERNAL_FLAGS, 'high')
+        self.simulator.go(WAIT_TIME)
+        routes = leader.get_routes()
+        self.check_num_of_routes(routes, num - 1, 0, 1)
+
         # Publish the same prefix on leader as an on-mesh prefix. Make
         # sure it is removed from external routes and now seen in the
         # prefix list.