add embedding model by default to distribution templates (#617)

# What does this PR do?
Adds the sentence transformer provider and the `all-MiniLM-L6-v2`
embedding model to the default models to register in the run.yaml for
all providers.

## Test Plan
llama stack build --template together --image-type conda
llama stack run
~/.llama/distributions/llamastack-together/together-run.yaml

llama_stack/templates/hf-endpoint/run-with-safety.yaml

@@ -18,6 +18,9 @@ providers:
     config:
       endpoint_name: ${env.INFERENCE_ENDPOINT_NAME}
       api_token: ${env.HF_API_TOKEN}
+  - provider_id: sentence-transformers
+    provider_type: inline::sentence-transformers
+    config: {}
   - provider_id: hf-endpoint-safety
     provider_type: remote::hf::endpoint
     config:
@@ -81,10 +84,18 @@ models:
   model_id: ${env.INFERENCE_MODEL}
   provider_id: hf-endpoint
   provider_model_id: null
+  model_type: llm
 - metadata: {}
   model_id: ${env.SAFETY_MODEL}
   provider_id: hf-endpoint-safety
   provider_model_id: null
+  model_type: llm
+- metadata:
+    embedding_dimension: 384
+  model_id: all-MiniLM-L6-v2
+  provider_id: sentence-transformers
+  provider_model_id: null
+  model_type: embedding
 shields:
 - params: null
   shield_id: ${env.SAFETY_MODEL}