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/language_models/src/provider/mistral.rs

@@ -816,6 +816,7 @@ mod tests {
             tool_choice: None,
             thread_id: None,
             prompt_id: None,
+            intent: None,
             mode: None,
             stop: Vec::new(),
         };