feat: generator schema migration

[cristianoventura]

Description

This PR adds migrations to the generator schema, ensuring that changes to its structure remain backward-compatible. This allows the generator to work properly even when the schema is updated.

The pattern adopted in this PR is based on the settings migration #371.

How to Test

• make changes to the latest version of the schema /schemas/generator/v1/index.ts such as renaming a property.
• change the migrate function in /schemas/generator/v0/index.ts to return the new schema.
• make appropriate changes to the remaining implementation so the new schema is used. This may require changing the slices and several other parts of the code.
• ensure the generator JSON file has version: '0' and all old properties before testing.
• open the old generator file and check that options were migrated.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (npm run lint) and all checks pass.
• I have run tests locally (npm test) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Screenshots (if appropriate):

Related PR(s)/Issue(s)

Resolves #370