collab: Add usages table to LLM database (#15884)

This PR adds a `usages` table to the LLM database.

We'll use this to track usage for rate-limiting purposes.

Release Notes:

- N/A

crates/collab/src/llm/db/ids.rs

@@ -3,5 +3,6 @@ use serde::{Deserialize, Serialize};
 
 use crate::id_type;
 
-id_type!(ProviderId);
 id_type!(ModelId);
+id_type!(ProviderId);
+id_type!(UsageId);