Add config output-handle-key/output-old-value doc for ticdc (#16812) (#…

…16868)

ticdc/ticdc-changefeed-config.md

@@ -193,6 +193,12 @@ enable-partition-separator = true
 # include-commit-ts = false
 # The encoding method of binary data, which can be 'base64' or 'hex'. The default value is 'base64'.
 # binary-encoding-method = 'base64'
+# Whether to output handle key information. The default value is false. 
+# This configuration parameter is for internal implementation only, so it is not recommended to set it.
+# output-handle-key = false
+# Whether to output the value before the row data changes. The default value is false. 
+# When it is enabled, the UPDATE event will output two rows of data: the first row is a DELETE event that outputs the data before the change; the second row is an INSERT event that outputs the changed data.
+# output-old-value = false
 
 # Starting from v8.0.0, TiCDC supports the Simple message encoding protocol. The following are the configuration parameters for the Simple protocol.
 # For more information about the protocol, see <https://docs.pingcap.com/tidb/stable/ticdc-simple-protocol>.