feat: define generated column on table/source whose schema is externally defined

[st1page]

Currently, we do not allow user to define schema in column clause

CREATE SOURCE(a int, b int) FORMAT PLAIN ENCODE PROTOBUF;
 ERROR: ExecuteError: Protocol error: User-defined schema is not allowed with FORMAT PLAIN ENCODE PROTOBUF

When the user wants to define a generated column, he must specify columns in the create source/table statement. We might need to introduce another syntax.

CREATE SOURCE(*, proc_time timestampz AS proctime()) FORMAT PLAIN ENCODE PROTOBUF;

[yuhao-su]

Should we allow writing filed names apart from * ?

Should we allow * written in other parts other than the very beginning?

[st1page]

Should we allow writing filed names apart from * ?

Should we allow * written in other parts other than the very beginning?

I think we can disallow them currently.