agent: Attach thread ID and prompt ID to telemetry events (#29069)

This PR attaches the thread ID and the new prompt ID to telemetry events
for completions in the Agent panel.

Release Notes:

- N/A

---------

Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>

crates/agent/src/active_thread.rs

@@ -1212,6 +1212,8 @@ impl ActiveThread {
                 }
 
                 let request = language_model::LanguageModelRequest {
+                    thread_id: None,
+                    prompt_id: None,
                     messages: vec![LanguageModelRequestMessage {
                         role: language_model::Role::User,
                         content: vec![content.into()],
@@ -1277,6 +1279,7 @@ impl ActiveThread {
         }
 
         self.thread.update(cx, |thread, cx| {
+            thread.advance_prompt_id();
             thread.send_to_model(model.model, RequestKind::Chat, cx)
         });
         cx.notify();