Replicate generated columns when 'publish_generated_columns' is set.

Replicate generated columns when 'publish_generated_columns' is set.

This patch builds on the work done in commit 745217a051 by enabling the
replication of generated columns alongside regular column changes through
a new publication parameter: publish_generated_columns.

Example usage:
CREATE PUBLICATION pub1 FOR TABLE tab_gencol WITH (publish_generated_columns = true);

The column list takes precedence. If the generated columns are specified
in the column list, they will be replicated even if
'publish_generated_columns' is set to false. Conversely, if generated
columns are not included in the column list (assuming the user specifies a
column list), they will not be replicated even if
'publish_generated_columns' is true.

Author: Vignesh C, Shubham Khanna
Reviewed-by: Peter Smith, Amit Kapila, Hayato Kuroda, Shlok Kyal, Ajin Cherian, Hou Zhijie, Masahiko Sawada
Discussion: https://postgr.es/m/B80D17B2-2C8E-4C7D-87F2-E5B4BE3C069E@gmail.com