Model Type Design: optional uri

[da-liii]

CREATE (OR REPLACE)? MODEL (IF NOT EXISTS)? model=qualifiedName
      (FLAVOR flavor=identifier)?
      (MODEL_TYPE modeltype=qualifiedName)?
      (OPTIONS optionList)?
      (RETURNS datatype=dataType)?
      (USING uri=STRING)

URI specifies how to load a model. Sometimes, we load a model in that way:

import ml_pkg

model = ml_pkg.ocr_model()
preds = model(inputs)

For the above use case, we do not need a model registry (or we need an anonymous model registry).

BootstrapModelType is also needed to verify if a ModelType can be bootstrapped.