pgsql: Add "pg_database_owner" default role.

Add "pg_database_owner" default role.

Membership consists, implicitly, of the current database owner. Expect
use in template databases. Once pg_database_owner has rights within a
template, each owner of a database instantiated from that template will
exercise those rights.

Reviewed by John Naylor.

Discussion: https://postgr.es/m/20201228043148.GA1053024@rfd.leadboat.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a14a0118a1fecf4066e53af52ed0f188607d0c4b

Modified Files
--------------
doc/src/sgml/catalogs.sgml | 3 ++
doc/src/sgml/user-manag.sgml | 15 ++++++++
src/backend/catalog/information_schema.sql | 9 ++++-
src/backend/commands/user.c | 36 ++++++++++++++++++
src/backend/utils/adt/acl.c | 44 ++++++++++++++++++++-
src/backend/utils/cache/catcache.c | 6 ++-
src/bin/psql/describe.c | 1 +
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_authid.dat | 5 +++
src/test/regress/expected/privileges.out | 61 ++++++++++++++++++++++++++++++
src/test/regress/sql/privileges.sql | 31 +++++++++++++++
11 files changed, 207 insertions(+), 6 deletions(-)