pgsql: Add ALTER TABLE ... ALTER CONSTRAINT ... SET [NO] INHERIT

Add ALTER TABLE ... ALTER CONSTRAINT ... SET [NO] INHERIT

This allows to redefine an existing non-inheritable constraint to be
inheritable, which allows to straighten up situations with NO INHERIT
constraints so that thay can become normal constraints without having to
re-verify existing data. For existing inheritance children this may
require creating additional constraints, if they don't exist already.

It also allows to do the opposite, if only for symmetry.

Author: Suraj Kharage <suraj(dot)kharage(at)enterprisedb(dot)com>
Reviewed-by: jian he <jian(dot)universality(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAF1DzPVfOW6Kk=7SSh7LbneQDJWh=PbJrEC_Wkzc24tHOyQWGg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f4e53e10b6ce0eedeb98caa4356facb47c7bb9cb

Modified Files
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doc/src/sgml/ref/alter_table.sgml | 23 +++++-
src/backend/commands/tablecmds.c | 115 +++++++++++++++++++++++++----
src/backend/parser/gram.y | 28 ++++++++
src/include/nodes/parsenodes.h | 2 +
src/test/regress/expected/inherit.out | 131 +++++++++++++++++++++++++++++++++-
src/test/regress/sql/inherit.sql | 79 +++++++++++++++++++-
6 files changed, 359 insertions(+), 19 deletions(-)