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/assistant/src/terminal_inline_assistant.rs

@@ -292,6 +292,8 @@ impl TerminalInlineAssistant {
         });
 
         Ok(LanguageModelRequest {
+            thread_id: None,
+            prompt_id: None,
             messages,
             tools: Vec::new(),
             stop: Vec::new(),