Add tool use support for OpenAI models (#28051)

This PR adds support for using tools to the OpenAI models.

Release Notes:

- agent: Added support for tool use with OpenAI models (Preview only).

crates/open_ai/src/open_ai.rs

@@ -2,7 +2,7 @@ mod supported_countries;
 
 use anyhow::{Context as _, Result, anyhow};
 use futures::{
-    AsyncBufReadExt, AsyncReadExt, Stream, StreamExt,
+    AsyncBufReadExt, AsyncReadExt, StreamExt,
     io::BufReader,
     stream::{self, BoxStream},
 };
@@ -618,14 +618,3 @@ pub fn embed<'a>(
         }
     }
 }
-
-pub fn extract_text_from_events(
-    response: impl Stream<Item = Result<ResponseStreamEvent>>,
-) -> impl Stream<Item = Result<String>> {
-    response.filter_map(|response| async move {
-        match response {
-            Ok(mut response) => Some(Ok(response.choices.pop()?.delta.content?)),
-            Err(error) => Some(Err(error)),
-        }
-    })
-}