Add db_migrator_constants.py script to setup.py (sonic-net#2534)

Author: vaibhavhd

setup.py

@@ -90,6 +90,7 @@
         'scripts/coredump-compress',
         'scripts/configlet',
         'scripts/db_migrator.py',
+        'scripts/db_migrator_constants.py',
         'scripts/decode-syseeprom',
         'scripts/dropcheck',
         'scripts/disk_check.py',