Add database_privileges.replace_for_roles RPC function.

[mathemancer]

Fixes #3773

Adds the database_privileges.replace_for_roles RPC function.

Technical details

The function is documented, and its use should be self-explanatory.

Screenshots

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[Anish9901]

Looks great, I've added a minor suggestion.

[Anish9901]

Suggested change

	msar.build_database_privilege_replace_expr(role_oid, direct),
	E';\n'
	) || ';'
	FROM jsonb_to_recordset(priv_spec) AS x(role_oid regrole, direct jsonb);
	msar.build_database_privilege_replace_expr(role_oid, privileges_),
	E';\n'
	) || ';'
	FROM jsonb_to_recordset(priv_spec) AS x(role_oid regrole, privileges_ jsonb);

[mathemancer]

I don't think this will work, will it? I'd need to check, but I'm pretty sure jsonb_to_recordset needs accurate key names in the AS clause. So, we need to leave it as direct to match with what we expect in the spec when called.

[mathemancer]

I checked. It won't work that way without either making some adapter in Python to convert the JSON between formats (do not want) or changing the API spec (also do not want).