Pass up intent with completion requests (#31710)

This PR adds a new `intent` field to completion requests to assist in
categorizing them correctly.

Release Notes:

- N/A

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

crates/semantic_index/src/summary_index.rs

@@ -560,6 +560,7 @@ impl SummaryIndex {
             thread_id: None,
             prompt_id: None,
             mode: None,
+            intent: None,
             messages: vec![LanguageModelRequestMessage {
                 role: Role::User,
                 content: vec![prompt.into()],