Model Zoo releases a second model with the same name would overwrite the first released model

[sneaxiy]

Suppose that we have trained a model with some hyperparameters and released it to the SQLFlow model zoo with the tag v0.1 and the name my_model:

sqlflow release model my_model v0.1

Then we train the model with other hyperparameters and release the trained model with a different tag v0.2 but the same name my_model.

sqlflow release model my_model v0.2

The latter released model would overwrite the former one even though the tag is different (v0.1 vs v0.2).

This bug should be fixed.