pgsql: Invalidate relcache when changing REPLICA IDENTITY index.

Invalidate relcache when changing REPLICA IDENTITY index.

When changing REPLICA IDENTITY INDEX to another one, the target table's
relcache was not being invalidated. This leads to skipping update/delete
operations during apply on the subscriber side as the columns required to
search corresponding rows won't get logged.

Author: Tang Haiying, Hou Zhijie
Reviewed-by: Euler Taveira, Amit Kapila
Backpatch-through: 10
Discussion: https://postgr.es/m/OS0PR01MB61133CA11630DAE45BC6AD95FB939@OS0PR01MB6113.jpnprd01.prod.outlook.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2c0443c595705b6eda1932e4b1b3debc2162986d

Modified Files
--------------
src/backend/commands/tablecmds.c | 6 +++
src/test/subscription/t/100_bugs.pl | 86 ++++++++++++++++++++++++++++++++++++-
2 files changed, 91 insertions(+), 1 deletion(-)