pgsql: Add test for MAINTAIN permission with pg_restore_extended_stats(

Add test for MAINTAIN permission with pg_restore_extended_stats()

Like its cousin functions for the restore of relation and attribute
stats, pg_restore_extended_stats() needs to be run by a user that is the
database owner or has MAINTAIN privileges on the table whose stats are
restored. This commit adds a regression test ensuring that MAINTAIN is
required when calling the function. This test also checks that a
ShareUpdateExclusive lock is taken on the table whose stats are
restored.

This has been split from the commit that has introduced
pg_restore_extended_stats(), for clarity.

Author: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/CADkLM=dpz3KFnqP-dgJ-zvRvtjsa8UZv8wDAQdqho=qN3kX0Zg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d9abd9e1050db4c2fcdce6fcd8dc0ede6769db16

Modified Files
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src/test/regress/expected/stats_import.out | 42 ++++++++++++++++++++++++++++++
src/test/regress/sql/stats_import.sql | 32 +++++++++++++++++++++++
2 files changed, 74 insertions(+)