pgsql: Fix replica identity check for MERGE.

Fix replica identity check for MERGE.

When executing a MERGE, check that the target relation supports all
actions mentioned in the MERGE command. Specifically, check that it
has a REPLICA IDENTITY if it publishes updates or deletes and the
MERGE command contains update or delete actions. Failing to do this
can silently break replication.

Author: Zhijie Hou <houzj(dot)fnst(at)fujitsu(dot)com>
Reviewed-by: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Reviewed-by: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Tested-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Discussion: https://postgr.es/m/OS3PR01MB57180C87E43A679A730482DF94B62@OS3PR01MB5718.jpnprd01.prod.outlook.com
Backpatch-through: 15

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fc6600fc1cd13b695fbde4b5f3ff0d2e97c36dea

Modified Files
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src/backend/executor/execMain.c | 11 ++++++++++-
src/test/regress/expected/publication.out | 28 ++++++++++++++++++++++++++++
src/test/regress/sql/publication.sql | 31 +++++++++++++++++++++++++++++++
3 files changed, 69 insertions(+), 1 deletion(-)