fix: Move sentence-transformers to the top (#2703)

Move sentence-transformers to be the first embedding in the list of
models. This ensures it will always be the default and is more
consistent then having the default change based on what env variables
are available

Closes: #2702

## Test Plan
Manually verified

Signed-off-by: Derek Higgins <derekh@redhat.com>

llama_stack/templates/starter/run.yaml

@@ -262,6 +262,11 @@ inference_store:
   type: sqlite
   db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/starter}/inference_store.db
 models:
+- metadata:
+    embedding_dimension: 384
+  model_id: all-MiniLM-L6-v2
+  provider_id: ${env.ENABLE_SENTENCE_TRANSFORMERS:=sentence-transformers}
+  model_type: embedding
 - metadata: {}
   model_id: ${env.ENABLE_CEREBRAS:=__disabled__}/llama3.1-8b
   provider_id: ${env.ENABLE_CEREBRAS:=__disabled__}
@@ -1168,11 +1173,6 @@ models:
   provider_id: ${env.ENABLE_SAMBANOVA:=__disabled__}
   provider_model_id: sambanova/Meta-Llama-Guard-3-8B
   model_type: llm
-- metadata:
-    embedding_dimension: 384
-  model_id: all-MiniLM-L6-v2
-  provider_id: ${env.ENABLE_SENTENCE_TRANSFORMERS:=sentence-transformers}
-  model_type: embedding
 shields:
 - shield_id: ${env.SAFETY_MODEL:=__disabled__}
   provider_shield_id: ${env.ENABLE_OLLAMA:=__disabled__}/${env.SAFETY_MODEL:=__disabled__}

llama_stack/templates/starter/starter.py

@@ -323,7 +323,7 @@ def get_distribution_template() -> DistributionTemplate:
                     "files": [files_provider],
                     "post_training": [post_training_provider],
                 },
-                default_models=default_models + [embedding_model],
+                default_models=[embedding_model] + default_models,
                 default_tool_groups=default_tool_groups,
                 # TODO: add a way to enable/disable shields on the fly
                 default_shields=shields,