feat(client/transport): enhance HTTP request flexibility

Enhanced the flexibility of HTTP requests in the streamable HTTP client by allowing additional headers to be specified. This change aims to support more diverse server requirements and improve the adaptability of our client transport layer.

Signed-off-by: Matthis Holleville <matthish29@gmail.com>

Author: matthisholleville

client/transport/streamable_http.go

@@ -752,7 +752,7 @@ func (c *StreamableHTTP) sendResponseToServer(ctx context.Context, response *JSO
 	ctx, cancel := c.contextAwareOfClientClose(ctx)
 	defer cancel()
 
-	resp, err := c.sendHTTP(ctx, http.MethodPost, bytes.NewReader(responseBody), "application/json, text/event-stream")
+	resp, err := c.sendHTTP(ctx, http.MethodPost, bytes.NewReader(responseBody), "application/json, text/event-stream", nil)
 	if err != nil {
 		c.logger.Errorf("failed to send response to server: %v", err)
 		return