Add support for the Google Search tool

- Gemini 2.0 and above use a google_search tool instead of a
google_search_retrieval tool. This commit adds support for the new tool.

examples/google-search.rs

@@ -0,0 +1,44 @@
+use gemini_rs::prelude::*;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    tracing_subscriber::fmt().init();
+    let authentication_manager = gcp_auth::provider().await?;
+    let api_endpoint = std::env::var("API_ENDPOINT")?;
+    let project_id = std::env::var("PROJECT_ID")?;
+    let location_id = std::env::var("LOCATION_ID")?;
+
+    let gemini = GeminiClient::new(
+        authentication_manager,
+        api_endpoint,
+        project_id,
+        location_id,
+    );
+
+    let prompt = "What day is today?";
+
+    let request = GenerateContentRequest {
+        contents: vec![Content {
+            role: Some(Role::User),
+            parts: Some(vec![Part::Text(prompt.to_string())]),
+        }],
+        tools: Some(vec![Tools {
+            google_search: Some(GoogleSearch::default()),
+            ..Default::default()
+        }]),
+        ..Default::default()
+    };
+
+    println!(
+        "Request: {}",
+        serde_json::to_string_pretty(&request).unwrap()
+    );
+
+    let result = gemini
+        .generate_content(&request, "gemini-2.0-flash-001")
+        .await?;
+
+    println!("Response: {:?}", result.candidates[0].get_text().unwrap());
+
+    Ok(())
+}