pgsql: Raise a warning if there is a possibility of data from multiple

Raise a warning if there is a possibility of data from multiple origins.

This commit raises a warning message for a combination of options
('copy_data = true' and 'origin = none') during CREATE/ALTER subscription
operations if the publication tables were also replicated from other
publishers.

During replication, we can skip the data from other origins as we have that
information in WAL but that is not possible during initial sync so we raise
a warning if there is such a possibility.

Author: Vignesh C
Reviewed-By: Peter Smith, Amit Kapila, Jonathan Katz, Shi yu, Wang wei
Discussion: https://www.postgresql.org/message-id/CALDaNm0gwjY_4HFxvvty01BOT01q_fJLKQ3pWP9=9orqubhjcQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/875693019053b8897ec3983e292acbb439b088c3

Modified Files
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doc/src/sgml/ref/alter_subscription.sgml  |   5 ++
doc/src/sgml/ref/create_subscription.sgml |  35 ++++++++
src/backend/commands/subscriptioncmds.c   | 133 ++++++++++++++++++++++++++++--
src/test/subscription/t/030_origin.pl     | 114 +++++++++++++++++++------
4 files changed, 258 insertions(+), 29 deletions(-)