feat(coprocessor): make multi-chain DB migration backwards compatible (#2043)

* feat(coprocessor): make multi-chain DB migration backwards compatible

Make sure both new and old versions can work with the same DB, should we
want to revert the new one to the old one.

* feat(coprocessor): add defaults needed for old code

* fix(coprocessor): fix zkproof-worker test DB field name

* fix(coprocessor): fix bad stress-test-generator DB field name

Author: dartdart26