collab: Rename symbols for existing Stripe synchronization (#29570)

This PR renames the symbols for the existing Stripe synchronization.

This will make things clearer once the new synchronization job for the
new billing is added.

Release Notes:

- N/A

crates/collab/src/stripe_billing.rs

@@ -268,7 +268,7 @@ impl StripeBilling {
         Ok(())
     }
 
-    pub async fn bill_model_usage(
+    pub async fn bill_model_token_usage(
         &self,
         customer_id: &stripe::CustomerId,
         model: &StripeModel,