feat: add chain method to create Request instance

examples/chat_completion.rs

@@ -4,29 +4,20 @@ use std::env;
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let client = Client::new(env::var("OPENAI_API_KEY").unwrap().to_string());
-    let req = ChatCompletionRequest {
-        model: chat_completion::GPT4.to_string(),
-        messages: vec![chat_completion::ChatCompletionMessage {
+
+    let req = ChatCompletionRequest::new(
+        chat_completion::GPT4.to_string(),
+        vec![chat_completion::ChatCompletionMessage {
             role: chat_completion::MessageRole::user,
             content: String::from("What is Bitcoin?"),
             name: None,
             function_call: None,
         }],
-        functions: None,
-        function_call: None,
-        temperature: None,
-        top_p: None,
-        n: None,
-        stream: None,
-        stop: None,
-        max_tokens: None,
-        presence_penalty: None,
-        frequency_penalty: None,
-        logit_bias: None,
-        user: None,
-    };
+    );
+
     let result = client.chat_completion(req)?;
     println!("{:?}", result.choices[0].message.content);
+
     Ok(())
 }