Add additional_instructions on openai assistan runs create. (#29164)

- **Description**: In the functions `_create_run` and `_acreate_run`,
the parameters passed to the creation of
`openai.resources.beta.threads.runs` were limited.

  Source: 
  ```
  def _create_run(self, input: dict) -> Any:
        params = {
            k: v
            for k, v in input.items()
            if k in ("instructions", "model", "tools", "run_metadata")
        }
        return self.client.beta.threads.runs.create(
            input["thread_id"],
            assistant_id=self.assistant_id,
            **params,
        )
  ```
- OpenAI Documentation
([createRun](https://platform.openai.com/docs/api-reference/runs/createRun))

- Full list of parameters `openai.resources.beta.threads.runs` ([source
code](https://github.com/openai/openai-python/blob/main/src/openai/resources/beta/threads/runs/runs.py#L91))

 
- **Issue:** Fix #17574 



- [x] **Lint and test**: Run `make format`, `make lint` and `make test`
from the root of the package(s) you've modified. See contribution
guidelines for more: https://python.langchain.com/docs/contributing/

Co-authored-by: ccurme <chester.curme@gmail.com>

libs/langchain/langchain/agents/openai_assistant/base.py

@@ -408,7 +408,8 @@ class OpenAIAssistantRunnable(RunnableSerializable[Dict, OutputType]):
                 message_metadata: Metadata to associate with a new message.
                 thread_metadata: Metadata to associate with new thread. Only relevant
                     when a new thread is created.
-                instructions: Additional run instructions.
+                instructions: Overrides the instructions of the assistant.
+                additional_instructions: Appends additional instructions.
                 model: Override Assistant model for this run.
                 tools: Override Assistant tools for this run.
                 run_metadata: Metadata to associate with new run.
@@ -507,7 +508,14 @@ class OpenAIAssistantRunnable(RunnableSerializable[Dict, OutputType]):
         params = {
             k: v
             for k, v in input.items()
-            if k in ("instructions", "model", "tools", "run_metadata")
+            if k
+            in (
+                "instructions",
+                "model",
+                "tools",
+                "additional_instructions",
+                "run_metadata",
+            )
         }
         return self.client.beta.threads.runs.create(
             input["thread_id"],
@@ -637,7 +645,14 @@ class OpenAIAssistantRunnable(RunnableSerializable[Dict, OutputType]):
         params = {
             k: v
             for k, v in input.items()
-            if k in ("instructions", "model", "tools", "run_metadata")
+            if k
+            in (
+                "instructions",
+                "model",
+                "tools",
+                "additional_instructions",
+                "run_metadata",
+            )
         }
         return await self.async_client.beta.threads.runs.create(
             input["thread_id"],