[PM-15179] Implement endpoints to add existing organization to CB provider (#5310)

* Implement endpoints to add existing organization to provider

* Run dotnet format

* Support MOE

* Run dotnet format

* Move ProviderClientsController under AC ownership

* Move ProviderClientsControllerTests under AC ownership

* Jared's feedback

util/Migrator/DbScripts/2025-01-28_00_Add_Organization_ReadAddableToProviderByUserId.sql

@@ -0,0 +1,31 @@
+-- Drop existing SPROC
+IF OBJECT_ID('[dbo].[Organization_ReadAddableToProviderByUserId') IS NOT NULL
+BEGIN
+    DROP PROCEDURE [dbo].[Organization_ReadAddableToProviderByUserId]
+END
+GO
+
+CREATE PROCEDURE [dbo].[Organization_ReadAddableToProviderByUserId]
+    @UserId UNIQUEIDENTIFIER,
+    @ProviderType TINYINT
+AS
+BEGIN
+    SET NOCOUNT ON
+    SELECT O.* FROM [dbo].[OrganizationUser] AS OU
+    JOIN [dbo].[Organization] AS O ON O.[Id] = OU.[OrganizationId]
+    WHERE
+        OU.[UserId] = @UserId AND
+        OU.[Type] = 0 AND
+        OU.[Status] = 2 AND
+        O.[Enabled] = 1 AND
+        O.[GatewayCustomerId] IS NOT NULL AND
+        O.[GatewaySubscriptionId] IS NOT NULL AND
+        O.[Seats] > 0 AND
+        O.[Status] = 1 AND
+        O.[UseSecretsManager] = 0 AND
+      -- All Teams & Enterprise for MSP
+        (@ProviderType = 0 AND O.[PlanType] IN (2, 3, 4, 5, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20) OR
+            -- All Enterprise for MOE
+         @ProviderType = 2 AND O.[PlanType] IN (4, 5, 10, 11, 14, 15, 19, 20));
+END
+GO