Release v9.0.0

[ty-porter]

Required

• [x] Config migration feature
• [ ] Happy path testing for the config migration feature
• [ ] Rework validate_config.py:
  • Should be read-only (changes must come from a migration)
  • Should correctly associate and validate custom configs to its associated schema (ex. config.json and config.alt.json belong to the same config family referencing config.schema.json)

Nice to Have

• [ ] Refactor -- centralize config path strings to a helper that associates configs in the same config family (avoid brittle string interpolation all over the codebase)