support adding alias for models without hf repo/sku entry

[dineshyv]

What does this PR do?

adds a new method build_model_alias_with_just_llama_model which is needed for cases like ollama's quantized models which do not really have a repo in hf and an entry in SKU list.

Test Plan

pytest -v -s -m "ollama" llama_stack/providers/tests/inference/test_text_inference.py