sql: support default privileges at the database level

[jseldess]

PR: cockroachdb/cockroach#66785

From release notes:

Added support for ALTER DEFAULT PRIVILEGES and default privileges stored on databases. All objects created in a database will have the privilege set defined by the default privileges for that type of object on the database. The types of objects are TABLES, SEQUENCES, SCHEMAS, TYPES. Example: ALTER DEFAULT PRIVILEGES GRANT SELECT ON TABLES TO foo makes it such that all tables created by the user that executed the ALTER DEFAULT PRIVILEGES command will have SELECT privilege on the table for user foo. Additionally, one can specify a role. Example: ALTER DEFAULT PRIVILEGES FOR ROLE bar GRANT SELECT ON TABLES TO foo. All tables created by bar will have SELECT privilege for foo. If a role is not specified, it uses the current user. For further context, see the PostgreSQL documentation. Currently, default privileges are not supported on the schema. Specifying a schema like ALTER DEFAULT PRIVILEGES IN SCHEMA s will error. WITH GRANT OPTION is ignored. GRANT OPTION FOR is also ignored. [#66785][#66785] {% comment %}doc{% endcomment %}