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For the `echo` and `pystr` engines we previously required the user to pass `--model-name <x>` so we would have a name for the model. If the input is HTTP we do need this to match on the users' JSON request.

If the input is Text we don't need a name. So if the input is Text and we don't already have a name for the model, give it one.

Co-authored-by: Harrison Saturley-Hall <454891+saturley-hall@users.noreply.github.com>
Co-authored-by: Harrison King Saturley-Hall <hsaturleyhal@nvidia.com>

Co-authored-by: Biswa Panda <biswa.panda@gmail.com>