collab: Add billing_subscriptions table (#15448)

This PR adds a new `billing_subscriptions` table to the database, as
well as some accompanying models/queries.

In this table we store a minimal amount of data from Stripe:

- The Stripe customer ID
- The Stripe subscription ID
- The status of the Stripe subscription

This should be enough for interactions with the Stripe API (e.g., to
[create a customer portal
session](https://docs.stripe.com/api/customer_portal/sessions/create)),
as well as determine whether a subscription is active (based on the
`status`).

Release Notes:

- N/A

crates/collab/src/db/queries/billing_subscriptions.rs

@@ -0,0 +1,55 @@
+use crate::db::billing_subscription::StripeSubscriptionStatus;
+
+use super::*;
+
+#[derive(Debug)]
+pub struct CreateBillingSubscriptionParams {
+    pub user_id: UserId,
+    pub stripe_customer_id: String,
+    pub stripe_subscription_id: String,
+    pub stripe_subscription_status: StripeSubscriptionStatus,
+}
+
+impl Database {
+    /// Creates a new billing subscription.
+    pub async fn create_billing_subscription(
+        &self,
+        params: &CreateBillingSubscriptionParams,
+    ) -> Result<()> {
+        self.transaction(|tx| async move {
+            billing_subscription::Entity::insert(billing_subscription::ActiveModel {
+                user_id: ActiveValue::set(params.user_id),
+                stripe_customer_id: ActiveValue::set(params.stripe_customer_id.clone()),
+                stripe_subscription_id: ActiveValue::set(params.stripe_subscription_id.clone()),
+                stripe_subscription_status: ActiveValue::set(params.stripe_subscription_status),
+                ..Default::default()
+            })
+            .exec_without_returning(&*tx)
+            .await?;
+
+            Ok(())
+        })
+        .await
+    }
+
+    /// Returns all of the active billing subscriptions for the user with the specified ID.
+    pub async fn get_active_billing_subscriptions(
+        &self,
+        user_id: UserId,
+    ) -> Result<Vec<billing_subscription::Model>> {
+        self.transaction(|tx| async move {
+            let subscriptions = billing_subscription::Entity::find()
+                .filter(
+                    billing_subscription::Column::UserId.eq(user_id).and(
+                        billing_subscription::Column::StripeSubscriptionStatus
+                            .eq(StripeSubscriptionStatus::Active),
+                    ),
+                )
+                .all(&*tx)
+                .await?;
+
+            Ok(subscriptions)
+        })
+        .await
+    }
+}