support adding alias for models without hf repo/sku entry (#481)

# 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

---------

Co-authored-by: Dinesh Yeduguru <dineshyv@fb.com>

llama_stack/providers/remote/inference/ollama/ollama.py

@@ -16,6 +16,7 @@ from ollama import AsyncClient
 
 from llama_stack.providers.utils.inference.model_registry import (
     build_model_alias,
+    build_model_alias_with_just_provider_model_id,
     ModelRegistryHelper,
 )
 
@@ -44,7 +45,7 @@ model_aliases = [
         "llama3.1:8b-instruct-fp16",
         CoreModelId.llama3_1_8b_instruct.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama3.1:8b",
         CoreModelId.llama3_1_8b_instruct.value,
     ),
@@ -52,7 +53,7 @@ model_aliases = [
         "llama3.1:70b-instruct-fp16",
         CoreModelId.llama3_1_70b_instruct.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama3.1:70b",
         CoreModelId.llama3_1_70b_instruct.value,
     ),
@@ -64,27 +65,27 @@ model_aliases = [
         "llama3.2:3b-instruct-fp16",
         CoreModelId.llama3_2_3b_instruct.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama3.2:1b",
         CoreModelId.llama3_2_1b_instruct.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama3.2:3b",
         CoreModelId.llama3_2_3b_instruct.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama-guard3:8b",
         CoreModelId.llama_guard_3_8b.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama-guard3:1b",
         CoreModelId.llama_guard_3_1b.value,
     ),
     build_model_alias(
-        "x/llama3.2-vision:11b-instruct-fp16",
+        "llama3.2-vision:11b-instruct-fp16",
         CoreModelId.llama3_2_11b_vision_instruct.value,
     ),
-    build_model_alias(
+    build_model_alias_with_just_provider_model_id(
         "llama3.2-vision",
         CoreModelId.llama3_2_11b_vision_instruct.value,
     ),

llama_stack/providers/utils/inference/model_registry.py

@@ -36,6 +36,16 @@ def build_model_alias(provider_model_id: str, model_descriptor: str) -> ModelAli
     )
 
 
+def build_model_alias_with_just_provider_model_id(
+    provider_model_id: str, model_descriptor: str
+) -> ModelAlias:
+    return ModelAlias(
+        provider_model_id=provider_model_id,
+        aliases=[],
+        llama_model=model_descriptor,
+    )
+
+
 class ModelRegistryHelper(ModelsProtocolPrivate):
     def __init__(self, model_aliases: List[ModelAlias]):
         self.alias_to_provider_id_map = {}