feat:litellm fallback configs

Author: Kabeer2004

src/server/litellm-config.yaml

@@ -1,8 +1,17 @@
 model_list:
   - model_name: gemini-2.5-flash
+    litellm_params:
+      model: gemini/gemini-2.5-flash
+      api_key: os.environ/GEMINI_API_KEY
+  - model_name: gemini-2.5-flash-fallback
+    litellm_params:
+      model: gemini/gemini-2.5-flash
+      api_key: os.environ/GEMINI_API_KEY_FALLBACK_1
+  - model_name: gemini-2.5-flash-lite
     litellm_params:
       model: gemini/gemini-2.5-flash-lite
       api_key: os.environ/GEMINI_API_KEY
 
 litellm_settings:
-  drop_params: true
+  drop_params: true
+  fallbacks: [{"gemini-2.5-flash": ["gemini-2.5-flash-fallback","gemini-2.5-flash-lite"]}]