fix(subsequences): better error from creation of features with incorrect params DEV-1441

[rgraber]

🗒️ Checklist

1. run linter locally
2. update developer docs (API, README, inline, etc.), if any
3. for user-facing doc changes create a Zulip thread at #Support Docs Updates, if any
4. draft PR with a title <type>(<scope>)<!>: <title> DEV-1234
5. assign yourself, tag PR: at least Front end and/or Back end or workflow
6. fill in the template below and delete template comments
7. review thyself: read the diff and repro the preview as written
8. open PR & confirm that CI passes & request reviewers, if needed
9. delete this section before merging

📣 Summary

Validate params before creating new advanced features.

👀 Preview steps

1. ℹ️ have an account and a project
2. `curl -X POST -H 'Authorization: Token ' http://kf.kobo.local/api/v2/assets/<asset_uid>/advanced-features --json '{"question_xpath": , "action": "manual_transcription", "params": [{"something":"bad"}]}'
3. 🔴 [on refactor-subsequences-2025] request 500s
4. 🟢 [on PR] request 400s