Set up correct OHE labels for subsets that use default model labels

[ejm714]

Fixes #234

229 introduced a bug whereby the new columns added to the labels file were in a different order than what is on the model. This PR fixes that by setting up the correct one hot encoded labels in the preprocess_labels validator rather than instantiate_model. Using the use_default_model_labels, we know whether the labels file should contain columns (with all zeroes) for species that are not present in the labels but are on the base model. Using a pd.Categorical before get_dummies allows us to generate these columns.

Running zamba train --config tests/assets/sample_train_config.yaml now works; the labels file has three species present in zamba but trains a model that outputs the full set of 32 labels.

[netlify[bot]]

✅ Deploy Preview for silly-keller-664934 ready!

Name	Link
🔨 Latest commit	0fdbc20af975645e989a7d22e8b2c365fbd9f304
🔍 Latest deploy log	https://app.netlify.com/sites/silly-keller-664934/deploys/63334834199b35000819d6d2
😎 Deploy Preview	https://deploy-preview-236--silly-keller-664934.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[github-actions[bot]]

🚀 Deployed on https://deploy-preview-236--silly-keller-664934.netlify.app

[codecov-commenter]

Codecov Report

Merging #236 (0fdbc20) into master (0a894a5) will increase coverage by 0.0%. The diff coverage is 100.0%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #236 +/- ## ====================================== Coverage 87.2% 87.2% ====================================== Files 28 28 Lines 1961 1962 +1 ====================================== + Hits 1710 1711 +1 Misses 251 251 ``` | [Impacted Files](https://codecov.io/gh/drivendataorg/zamba/pull/236?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=drivendataorg) | Coverage Δ | | |---|---|---| | [zamba/models/model\_manager.py](https://codecov.io/gh/drivendataorg/zamba/pull/236/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=drivendataorg#diff-emFtYmEvbW9kZWxzL21vZGVsX21hbmFnZXIucHk=) | `84.3% <ø> (-0.5%)` | :arrow_down: | | [zamba/models/config.py](https://codecov.io/gh/drivendataorg/zamba/pull/236/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=drivendataorg#diff-emFtYmEvbW9kZWxzL2NvbmZpZy5weQ==) | `96.9% <100.0%> (+<0.1%)` | :arrow_up: | | [zamba/models/utils.py](https://codecov.io/gh/drivendataorg/zamba/pull/236/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=drivendataorg#diff-emFtYmEvbW9kZWxzL3V0aWxzLnB5) | `100.0% <100.0%> (ø)` | |