Restore model validation check

[stevemessick]

In version 1.7.4.5 there were two definitions of this method. Someone (probably me) cleaned that up but deleted the second version, whereas the first was the one that was not being used.

Fixes #900

[rosbo]

The "model string" is only {owner}/{model-slug}. The model instance string is {owner}/{model-slug}/{framework}/{variation-slug}/{version-number}. The validate_model_instance_string function should be used for the later. We should not update validate_model_string.

Your issue is that sometimes, the wrong one is called.

There are 2 calls to validate_model_string.

• From the split_model_string function.
  • split_model_string is called multiple times. Sometimes, it called on a model instance string, other times on a model string. You should fix that to ensure each one calls the proper method.
• In kernel_push to validate a model data source: https://github.com/Kaggle/kaggle-api/blob/39d6de9e99948db2f23f46dad57971d995e3481c/src/kaggle/api/kaggle_api_extended.py#L3044. Here, I believe the model data source is actually a model instance so the other method should be called (you should confirm and test).