Make package flags available in SQL as constants

[AMDmi3]

Currently we have to use magic numbers like (1 << 16) when referencing Package flags. This is bad and inconvenient practice, so we should make constants available in SQL code somehow. There are 2 ways:

• SQL functions like

CREATE FUNCTION PackageFlag_VULNERABLE()
  RETURNS int LANGUAGE sql IMMUTABLE PARALLEL SAFE AS
'SELECT 1 << 16';

SELECT * FROM packages WHERE (flags & PackageFlag_VULNERABLE())::boolean;

• Template values

SELECT * FROM packages WHERE (flags & {{ PackageFlag.VULNERABLE }} )::boolean;