Docs: Add how to dispatch custom callback events (#24278)

* Add how-to guide for dispatching custom callback events.
* Add links from index to the how to guide
* Add link from streaming from within a tool
* Update versionadded to correct release
https://github.com/langchain-ai/langchain/releases/tag/langchain-core%3D%3D0.2.15

libs/core/langchain_core/callbacks/base.py

@@ -392,7 +392,7 @@ class RunManagerMixin:
             metadata: The metadata associated with the custom event
                 (includes inherited metadata).
 
-        .. versionadded:: 0.2.14
+        .. versionadded:: 0.2.15
         """
 
 
@@ -851,7 +851,7 @@ class AsyncCallbackHandler(BaseCallbackHandler):
             metadata: The metadata associated with the custom event
                 (includes inherited metadata).
 
-        .. versionadded:: 0.2.14
+        .. versionadded:: 0.2.15
         """
 
 

libs/core/langchain_core/callbacks/manager.py

@@ -2341,7 +2341,7 @@ async def adispatch_custom_event(
         LangChain from automatically propagating the config object on the user's
         behalf.
 
-    .. versionadded:: 0.2.14
+    .. versionadded:: 0.2.15
     """
     from langchain_core.runnables.config import (
         ensure_config,
@@ -2410,7 +2410,7 @@ def dispatch_custom_event(
             foo_ = RunnableLambda(foo)
             foo_.invoke({"a": "1"}, {"callbacks": [CustomCallbackManager()]})
 
-    .. versionadded:: 0.2.14
+    .. versionadded:: 0.2.15
     """
     from langchain_core.runnables.config import (
         ensure_config,

libs/core/langchain_core/runnables/schema.py

@@ -159,7 +159,7 @@ class StandardStreamEvent(BaseStreamEvent):
 class CustomStreamEvent(BaseStreamEvent):
     """Custom stream event created by the user.
 
-    .. versionadded:: 0.2.14
+    .. versionadded:: 0.2.15
     """
 
     # Overwrite the event field to be more specific.