collab: Add kind and period start/end timestamps to billing_subscriptions (#28796)

This PR updates the `billing_subscriptions` table with some new columns

- `kind` - The kind of the description (used to denote Zed Pro vs
existing)
- `stripe_current_period_start` - The Stripe timestamp of when the
subscriptions current period starts
- `stripe_current_period_end` - The Stripe timestamp of when the
subscriptions current period ends

Release Notes:

- N/A

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/collab/src/db/tables/billing_subscription.rs

@@ -9,10 +9,13 @@ pub struct Model {
     #[sea_orm(primary_key)]
     pub id: BillingSubscriptionId,
     pub billing_customer_id: BillingCustomerId,
+    pub kind: Option<SubscriptionKind>,
     pub stripe_subscription_id: String,
     pub stripe_subscription_status: StripeSubscriptionStatus,
     pub stripe_cancel_at: Option<DateTime>,
     pub stripe_cancellation_reason: Option<StripeCancellationReason>,
+    pub stripe_current_period_start: Option<i64>,
+    pub stripe_current_period_end: Option<i64>,
     pub created_at: DateTime,
 }
 
@@ -34,6 +37,14 @@ impl Related<super::billing_customer::Entity> for Entity {
 
 impl ActiveModelBehavior for ActiveModel {}
 
+#[derive(Eq, PartialEq, Copy, Clone, Debug, EnumIter, DeriveActiveEnum, Hash, Serialize)]
+#[sea_orm(rs_type = "String", db_type = "String(StringLen::None)")]
+#[serde(rename_all = "snake_case")]
+pub enum SubscriptionKind {
+    #[sea_orm(string_value = "zed_pro")]
+    ZedPro,
+}
+
 /// The status of a Stripe subscription.
 ///
 /// [Stripe docs](https://docs.stripe.com/api/subscriptions/object#subscription_object-status)