[Feature]: Support `npx rstest migrate`

[gaoachao]

What problem does this feature solve?

Support migration CLI with one-click setup.

What does the proposed API look like?

npx rstest migrate or npx rstest --migrate

[9aoy]

Currently, there are no plans to support migration CLI. Rstest will provide documentation for migrating once the API and configuration are relatively stable.

[chenjiahan]

Maybe we can provide example prompt and let AI to do the migration in the future.