docs: add changelog for PR 13434

changes/feat-13434.en.md

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+Simplified `rpc` configs.
+
+- New config `rpc.server_port` is added to replace `rpc.tcp_server_port` and `rpc.ssl_server_port`.
+- `rpc.tcp_client_num` is renamed to `rpc.client_num` since this config is for both TCP and SSL.
+
+The old config names are kept as aliases for backward compatibility.