collab: Make the StripeBilling object long-lived (#19090)

This PR makes the `StripeBilling` object long-lived so that we can make
better use of the cached data on it.

We now hold it on the `AppState` and spawn a background task to
initialize the cache on startup.

Release Notes:

- N/A

Co-authored-by: Richard <richard@zed.dev>

crates/collab/src/main.rs

@@ -111,6 +111,13 @@ async fn main() -> Result<()> {
 
                 let state = AppState::new(config, Executor::Production).await?;
 
+                if let Some(stripe_billing) = state.stripe_billing.clone() {
+                    let executor = state.executor.clone();
+                    executor.spawn_detached(async move {
+                        stripe_billing.initialize().await.trace_err();
+                    });
+                }
+
                 if mode.is_collab() {
                     state.db.purge_old_embeddings().await.trace_err();
                     RateLimiter::save_periodically(