doc: Fix misleading synopsis for CREATE/ALTER PUBLICATION.

doc: Fix misleading synopsis for CREATE/ALTER PUBLICATION.

The documentation for CREATE/ALTER PUBLICATION previously showed:

        [ ONLY ] table_name [ * ] [ ( column_name [, ... ] ) ] [ WHERE ( expression ) ] [, ... ]

to indicate that the table/column specification could be repeated.
However, placing [, ... ] directly after a multi-part construct was
misleading and made it unclear which portion was repeatable.

This commit introduces a new term, table_and_columns, to represent:

        [ ONLY ] table_name [ * ] [ ( column_name [, ... ] ) ] [ WHERE ( expression ) ]

and updates the synopsis to use:

        table_and_columns [, ... ]

which clearly identifies the repeatable element.

Backpatched to v15, where the misleading syntax was introduced.

Author: Peter Smith <smithpb2250@gmail.com>
Reviewed-by: Chao Li <lic@highgo.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CAHut+PtsyvYL3KmA6C8f0ZpXQ=7FEqQtETVy-BOF+cm9WPvfMQ@mail.gmail.com
Backpatch-through: 15