Support NO INHERIT modifier on CHECK constraints

[LucaCappelletti94]

PostgreSQL marks constraints that child tables should not inherit with NO INHERIT, and pg_dump emits it for any schema using table inheritance. The parser rejected it in every position:

ALTER TABLE docs ADD CONSTRAINT c CHECK (id > 0) NO INHERIT;
-- Expected: end of statement, found: NO

CREATE TABLE t (a INT, CONSTRAINT c CHECK (a > 0) NO INHERIT);
-- Expected: ',' or ')' after column definition, found: NO

Relevant doc: https://www.postgresql.org/docs/current/sql-createtable.html

[LucaCappelletti94]

@iffyio Also this one is pretty small

[iffyio]

LGTM! Thanks @LucaCappelletti94!