Add chat gpt api

examples/chat_completion.rs

@@ -0,0 +1,21 @@
+use openai_api_rs::v1::api::Client;
+use openai_api_rs::v1::chat_completion::{self, ChatCompletionRequest};
+use std::env;
+
+#[tokio::main]
+async 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::GPT3_5_TURBO.to_string(),
+        messages: vec![chat_completion::ChatCompletionMessage {
+            role: chat_completion::MessageRole::user,
+            content: String::from("NFTとは？"),
+        }],
+    };
+    let result = client.chat_completion(req).await?;
+    println!("{:?}", result.choices[0].message.content);
+
+    Ok(())
+}
+
+// OPENAI_API_KEY=xxxx cargo run --package openai-api-rs --example chat_completion