add support for using custom upstream llm (#365)

docs/source/resources/includes/arch_config_full_reference.yaml

@@ -31,7 +31,7 @@ endpoints:
 # Centralized way to manage LLMs, manage keys, retry logic, failover and limits in a central way
 llm_providers:
   - name: OpenAI
-    provider: openai
+    provider_interface: openai
     access_key: $OPENAI_API_KEY
     model: gpt-4o
     default: true
@@ -46,12 +46,12 @@ llm_providers:
         unit: minute
 
   - name: Mistral8x7b
-    provider: mistral
+    provider_interface: openai
     access_key: $MISTRAL_API_KEY
     model: mistral-8x7b
 
   - name: MistralLocal7b
-    provider: local
+    provider_interface: openai
     model: mistral-7b-instruct
     endpoint: mistral_local