Logical Replication - improve error message while adding tables to the publication in check_publication_add_relation

Hi,

While providing thoughts on [1], I observed that the error messages
that are emitted while adding foreign, temporary and unlogged tables
can be improved a bit from the existing [2] to [3]. For instance, the
existing message when foreign table is tried to add into the
publication "f1" is not a table" looks odd. Because it says that the
foreign table is not a table at all.

Attaching a small patch. Thoughts?

[1] - https://www.postgresql.org/message-id/CALj2ACWAxO3vSToT0o5nXL%3Drz5cNx90zaV-at%3DcvM14Tag4%3DcQ%40mail.gmail.com
[2] - t1 is a temporary table:
postgres=# CREATE PUBLICATION testpub FOR TABLE t1;
ERROR: table "t1" cannot be replicated
DETAIL: Temporary and unlogged relations cannot be replicated.

t1 is an unlogged table:
postgres=# CREATE PUBLICATION testpub FOR TABLE t1;
ERROR: table "t1" cannot be replicated
DETAIL: Temporary and unlogged relations cannot be replicated.

f1 is a foreign table:
postgres=# CREATE PUBLICATION testpub FOR TABLE f1;
ERROR: "f1" is not a table
DETAIL: Only tables can be added to publications.

[3] - t1 is a temporary table:
postgres=# CREATE PUBLICATION testpub FOR TABLE t1;
ERROR: temporary table "t1" cannot be replicated
DETAIL: Temporary, unlogged and foreign relations cannot be replicated.

t1 is an unlogged table:
postgres=# CREATE PUBLICATION testpub FOR TABLE t1;
ERROR: unlogged table "t1" cannot be replicated
DETAIL: Temporary, unlogged and foreign relations cannot be replicated.

f1 is a foreign table:
postgres=# CREATE PUBLICATION testpub FOR TABLE f1;
ERROR: foreign table "f1" cannot be replicated
DETAIL: Temporary, unlogged and foreign relations cannot be replicated.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com