[AC-1904] Implement endpoint to retrieve Provider subscription (#3921)

* Refactor Core.Billing prior to adding new logic

* Add ProviderBillingQueries.GetSubscriptionData

* Add ProviderBillingController.GetSubscriptionAsync

src/Core/Billing/Queries/Implementations/SubscriberQueries.cs

@@ -0,0 +1,61 @@
+using Bit.Core.Entities;
+using Bit.Core.Services;
+using Microsoft.Extensions.Logging;
+using Stripe;
+
+using static Bit.Core.Billing.Utilities;
+
+namespace Bit.Core.Billing.Queries.Implementations;
+
+public class SubscriberQueries(
+    ILogger<SubscriberQueries> logger,
+    IStripeAdapter stripeAdapter) : ISubscriberQueries
+{
+    public async Task<Subscription> GetSubscription(
+        ISubscriber subscriber,
+        SubscriptionGetOptions subscriptionGetOptions = null)
+    {
+        ArgumentNullException.ThrowIfNull(subscriber);
+
+        if (string.IsNullOrEmpty(subscriber.GatewaySubscriptionId))
+        {
+            logger.LogError("Cannot cancel subscription for subscriber ({ID}) with no GatewaySubscriptionId.", subscriber.Id);
+
+            return null;
+        }
+
+        var subscription = await stripeAdapter.SubscriptionGetAsync(subscriber.GatewaySubscriptionId, subscriptionGetOptions);
+
+        if (subscription != null)
+        {
+            return subscription;
+        }
+
+        logger.LogError("Could not find Stripe subscription ({ID}) to cancel.", subscriber.GatewaySubscriptionId);
+
+        return null;
+    }
+
+    public async Task<Subscription> GetSubscriptionOrThrow(ISubscriber subscriber)
+    {
+        ArgumentNullException.ThrowIfNull(subscriber);
+
+        if (string.IsNullOrEmpty(subscriber.GatewaySubscriptionId))
+        {
+            logger.LogError("Cannot cancel subscription for subscriber ({ID}) with no GatewaySubscriptionId.", subscriber.Id);
+
+            throw ContactSupport();
+        }
+
+        var subscription = await stripeAdapter.SubscriptionGetAsync(subscriber.GatewaySubscriptionId);
+
+        if (subscription != null)
+        {
+            return subscription;
+        }
+
+        logger.LogError("Could not find Stripe subscription ({ID}) to cancel.", subscriber.GatewaySubscriptionId);
+
+        throw ContactSupport();
+    }
+}