[BUG] DeleteModelStep and DeleteAgentStep don't handle NOT_FOUND exceptions

[dbwiddis]

What is the bug?

When deleting a connector, the Delete action is called directly without checking for existence of the connector; the DeleteResponse includes a DocWriteReponse.NOT_FOUND specifically to handle this use case.

However, for deleting models and deleting agents, ML Commons does a Get first (to check for various other reasons we can not delete) and in the case of the model/agent not being found, throws an exception instead.

Thus it is impossible to deprovision a model or agent that does not exist.

How can one reproduce the bug?

1. Provision a workflow that creates a model and/or agent.
2. Manually delete the model and/or agent with ML Commons API
3. Attempt to deprovision the workflow.

What is the expected behavior?

NOT_FOUND is not an error when deleting, and the resource is removed.