Add/Remove Tags to Model Projects

• Allow creation/deletion of model tags on new and existing models, eg:

# on model creation
model = client.create_model(name="foo_model", reference_id="foo-model-ref", tags=["some tag"])
# on existing models
existing_model = client.models[0]
existing_model.add_tags(['tag a', 'tag b'])
# remove tag
existing_model.remove_tags(['tag a'])