django 5.1, python 3.13, postgres 17 support

• added django 5.1 support
• added python 3.13 support
• added postgres 17 support
• marked postgres 12 support as deprecated
• marked postgres 13 support as deprecated
• dropped django 3.2 support
• dropped django 4.0 support
• dropped django 4.1 support
• dropped python 3.6 support
• dropped python 3.7 support
• dropped migrate_isnotnull_check_constraints command