Migrate encrypted data in database to new encryption structure

[dmjb]

Please describe the enhancement

See design doc in epic

Solution Proposal

In migration tool:

1. Change decrypt code to read from new fields then old fields
2. Begin writing new secrets to new structure only
3. Get each secret
4. Decrypt
5. Re-salt and re-encrypt using new structure
6. Validate that migration has worked and drop old column

Describe alternatives you've considered

No response

Additional context

No response

Acceptance Criteria

No response