improve error msg for CDC source with generated columns

[xxchan]

Describe the bug

I think this should be rejected, but the error message is very confusing.

dev=>  CREATE SOURCE pg_mydb (*, x timestamp as proctime()) WITH (
connector = 'postgres-cdc',
hostname = 'localhost',
port = '5432',
username = 'xxchan',
password = 'test',
database.name = 'postgres',
slot.name = 'mydb_slot'
);
ERROR:  Failed to run the query

Caused by:
  Protocol error: Row format for CDC connectors should be either omitted or set to `FORMAT PLAIN ENCODE JSON`, got: Debezium Json

If I add FORMAT PLAIN ENCODE JSON according to the error

dev=>  CREATE SOURCE pg_mydb (*, x timestamp as proctime()) WITH (
connector = 'postgres-cdc',
hostname = 'localhost',
port = '5432',
username = 'xxchan',
password = 'test',
database.name = 'postgres',
slot.name = 'mydb_slot'
) FORMAT PLAIN ENCODE JSON;
ERROR:  Failed to run the query

Caused by:
  sql parser error: Row format for CDC connectors should be either omitted or set to `FORMAT DEBEZIUM ENCODE JSON`

If I add FORMAT DEBEZIUM ENCODE JSON according to the error

dev=>  CREATE SOURCE pg_mydb (*, x timestamp as proctime()) WITH (
connector = 'postgres-cdc',
hostname = 'localhost',
port = '5432',
username = 'xxchan',
password = 'test',
database.name = 'postgres',
slot.name = 'mydb_slot'
) FORMAT DEBEZIUM ENCODE JSON;
ERROR:  Failed to run the query

Caused by:
  Protocol error: Row format for CDC connectors should be either omitted or set to `FORMAT PLAIN ENCODE JSON`, got: Debezium Json

Error message/log

No response

To Reproduce

No response

Expected behavior

No response

How did you deploy RisingWave?

No response

The version of RisingWave

latest main

Additional context

No response