Release v9.0.0

[ty-porter]

Required

• 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)

[WardBrian]

I can give the config changes and migration code a once over soon if you’re hoping to do this release during the offseason still

[ty-porter]

@WardBrian Sounds good. The migration code should be in a decent place. I will update the PR description for what else I'm planning before I consider this ready to release