collab: Fix issues with syncing LLM usage to Stripe (#18970)

This PR fixes some issues with our previous approach to synching LLM
usage over to Stripe.

We now have a separate LLM access price in Stripe that is a marker price
to allow us to create the initial subscription with that as its
subscription item

We then dynamically set the LLM usage price during the reconciliation
sync based on the usage for the current month.

Release Notes:

- N/A

---------

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

crates/collab/src/lib.rs

@@ -176,6 +176,7 @@ pub struct Config {
     pub slack_panics_webhook: Option<String>,
     pub auto_join_channel_id: Option<ChannelId>,
     pub stripe_api_key: Option<String>,
+    pub stripe_llm_access_price_id: Option<Arc<str>>,
     pub stripe_llm_usage_price_id: Option<Arc<str>>,
     pub supermaven_admin_api_key: Option<Arc<str>>,
     pub user_backfiller_github_access_token: Option<Arc<str>>,
@@ -237,6 +238,7 @@ impl Config {
             migrations_path: None,
             seed_path: None,
             stripe_api_key: None,
+            stripe_llm_access_price_id: None,
             stripe_llm_usage_price_id: None,
             supermaven_admin_api_key: None,
             user_backfiller_github_access_token: None,