docs(call_hooks.md): add docs on pre-call hooks

docs/my-website/docs/proxy/call_hooks.md

@@ -0,0 +1,78 @@
+# Call Hooks - Modify Data
+
+Modify data just before making litellm completion calls call on proxy
+
+See a complete example with our [parallel request rate limiter](https://github.com/BerriAI/litellm/blob/main/litellm/proxy/hooks/parallel_request_limiter.py)
+
+## Quick Start
+
+1. In your Custom Handler add a new `async_pre_call_hook` function
+
+This function is called just before a litellm completion call is made, and allows you to modify the data going into the litellm call [**See Code**](https://github.com/BerriAI/litellm/blob/589a6ca863000ba8e92c897ba0f776796e7a5904/litellm/proxy/proxy_server.py#L1000)
+
+```python
+from litellm.integrations.custom_logger import CustomLogger
+import litellm
+
+# This file includes the custom callbacks for LiteLLM Proxy
+# Once defined, these can be passed in proxy_config.yaml
+class MyCustomHandler(CustomLogger): # https://docs.litellm.ai/docs/observability/custom_callback#callback-class
+    # Class variables or attributes
+    def __init__(self):
+        pass
+
+    #### ASYNC #### 
+    
+    async def async_log_stream_event(self, kwargs, response_obj, start_time, end_time):
+        pass
+
+    async def async_log_pre_api_call(self, model, messages, kwargs):
+        pass
+
+    async def async_log_success_event(self, kwargs, response_obj, start_time, end_time):
+        pass
+
+    async def async_log_failure_event(self, kwargs, response_obj, start_time, end_time):
+        pass
+
+    #### CALL HOOKS - proxy only #### 
+
+    async def async_pre_call_hook(self, user_api_key_dict: UserAPIKeyAuth, cache: DualCache, data: dict, call_type: Literal["completion", "embeddings"]):
+        data["model"] = "my-new-model"
+        return data 
+
+proxy_handler_instance = MyCustomHandler()
+```
+
+2. Add this file to your proxy config
+
+```yaml
+model_list:
+  - model_name: gpt-3.5-turbo
+    litellm_params:
+      model: gpt-3.5-turbo
+
+litellm_settings:
+  callbacks: custom_callbacks.proxy_handler_instance # sets litellm.callbacks = [proxy_handler_instance]
+```
+
+3. Start the server + test the request
+
+```shell
+$ litellm /path/to/config.yaml
+```
+```shell
+curl --location 'http://0.0.0.0:8000/chat/completions' \
+    --data ' {
+    "model": "gpt-3.5-turbo",
+    "messages": [
+        {
+        "role": "user",
+        "content": "good morning good sir"
+        }
+    ],
+    "user": "ishaan-app",
+    "temperature": 0.2
+    }'
+```
+

docs/my-website/sidebars.js

@@ -102,6 +102,7 @@ const sidebars = {
         "proxy/load_balancing", 
         "proxy/virtual_keys",
         "proxy/model_management",
+        "proxy/call_hooks",
         "proxy/caching",
         "proxy/logging", 
         "proxy/cli",