Report response latency and errors when using (inline) assistant (#11806)

Release Notes:

- N/A

Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: David <davidsp@anthropic.com>

crates/telemetry_events/src/telemetry_events.rs

@@ -1,6 +1,6 @@
 use semantic_version::SemanticVersion;
 use serde::{Deserialize, Serialize};
-use std::{fmt::Display, sync::Arc};
+use std::{fmt::Display, sync::Arc, time::Duration};
 
 #[derive(Serialize, Deserialize, Debug)]
 pub struct EventRequestBody {
@@ -93,6 +93,8 @@ pub struct AssistantEvent {
     pub conversation_id: Option<String>,
     pub kind: AssistantKind,
     pub model: String,
+    pub response_latency: Option<Duration>,
+    pub error_message: Option<String>,
 }
 
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]