collab: Attach additional properties to Language Model Used event (#21770)

This PR attaches two new properties to the `Language Model Used` event:

- `has_llm_subscription` - This will tell us if a user is a paid
subscriber.
- `max_monthly_spend_in_cents` - This will indicate what their maximum
monthly spend is set to.

Release Notes:

- N/A

crates/collab/src/llm.rs

@@ -744,6 +744,8 @@ impl<S> Drop for TokenCountingStream<S> {
                 );
 
                 let properties = json!({
+                    "has_llm_subscription": claims.has_llm_subscription,
+                    "max_monthly_spend_in_cents": claims.max_monthly_spend_in_cents,
                     "plan": match claims.plan {
                         Plan::Free => "free".to_string(),
                         Plan::ZedPro => "zed_pro".to_string(),