pgsql: Fix propagation of persistence to sequences in ALTER TABLE / ADD

Fix propagation of persistence to sequences in ALTER TABLE / ADD COLUMN

Fix for 344d62fb9a9: That commit introduced unlogged sequences and
made it so that identity/serial sequences automatically get the
persistence level of their owning table. But this works only for
CREATE TABLE and not for ALTER TABLE / ADD COLUMN. The latter would
always create the sequence as logged (default), independent of the
persistence setting of the table. This is fixed here.

Note: It is allowed to change the persistence of identity sequences
directly using ALTER SEQUENCE. So mistakes in existing databases can
be fixed manually.

Reviewed-by: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/c4b6e2ed-bcdf-4ea7-965f-e49761094827%40eisentraut.org

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d17a3a4c6a34f61a3d4d9faa7a70c14d8d0c0ffb

Modified Files
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src/backend/parser/parse_utilcmd.c | 11 +++++-
src/test/regress/expected/identity.out | 72 ++++++++++++++++++++++++++++++++++
src/test/regress/sql/identity.sql | 18 +++++++++
3 files changed, 100 insertions(+), 1 deletion(-)