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/semantic_index/src/summary_index.rs

@@ -557,6 +557,8 @@ impl SummaryIndex {
         );
 
         let request = LanguageModelRequest {
+            thread_id: None,
+            prompt_id: None,
             messages: vec![LanguageModelRequestMessage {
                 role: Role::User,
                 content: vec![prompt.into()],