Add plugin usage telemetry (#14531)

adding metrics including: 
* plugin used
* plugin installed/uninstalled
* plugin enabled/disabled

codex-rs/app-server/tests/common/analytics_server.rs

@@ -0,0 +1,16 @@
+use anyhow::Result;
+use wiremock::Mock;
+use wiremock::MockServer;
+use wiremock::ResponseTemplate;
+use wiremock::matchers::method;
+use wiremock::matchers::path;
+
+pub async fn start_analytics_events_server() -> Result<MockServer> {
+    let server = MockServer::start().await;
+    Mock::given(method("POST"))
+        .and(path("/codex/analytics-events/events"))
+        .respond_with(ResponseTemplate::new(200))
+        .mount(&server)
+        .await;
+    Ok(server)
+}