[PM-28260] Optimize bulk reinvite endpoint (#6670)

* Implement optimized bulk invite resend command

- Added IBulkResendOrganizationInvitesCommand interface to define the bulk resend operation.
- Created BulkResendOrganizationInvitesCommand class to handle the logic for resending invites to multiple organization users.
- Integrated logging and validation to ensure only valid users receive invites.
- Included error handling for non-existent organizations and invalid user statuses.

* Add unit tests for BulkResendOrganizationInvitesCommand

- Implemented comprehensive test cases for the BulkResendOrganizationInvitesCommand class.
- Validated user statuses and ensured correct handling of valid and invalid users during bulk invite resends.
- Included tests for scenarios such as organization not found and empty user lists.
- Utilized Xunit and NSubstitute for effective testing and mocking of dependencies.

* Add IBulkResendOrganizationInvitesCommand to service collection

- Registered IBulkResendOrganizationInvitesCommand in the service collection for dependency injection.

* Update OrganizationUsersController to utilize IBulkResendOrganizationInvitesCommand

- Added IBulkResendOrganizationInvitesCommand to the OrganizationUsersController for handling bulk invite resends based on feature flag.
- Updated BulkReinvite method to conditionally use the new command or the legacy service based on the feature flag status.
- Enhanced unit tests to verify correct command usage depending on feature flag state, ensuring robust testing for both scenarios.

src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/InviteUsers/BulkResendOrganizationInvitesCommand.cs

@@ -0,0 +1,69 @@
+using Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.InviteUsers.Models;
+using Bit.Core.AdminConsole.Utilities.DebuggingInstruments;
+using Bit.Core.Entities;
+using Bit.Core.Enums;
+using Bit.Core.Exceptions;
+using Bit.Core.Repositories;
+using Microsoft.Extensions.Logging;
+
+namespace Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.InviteUsers;
+
+public class BulkResendOrganizationInvitesCommand : IBulkResendOrganizationInvitesCommand
+{
+    private readonly IOrganizationUserRepository _organizationUserRepository;
+    private readonly IOrganizationRepository _organizationRepository;
+    private readonly ISendOrganizationInvitesCommand _sendOrganizationInvitesCommand;
+    private readonly ILogger<BulkResendOrganizationInvitesCommand> _logger;
+
+    public BulkResendOrganizationInvitesCommand(
+        IOrganizationUserRepository organizationUserRepository,
+        IOrganizationRepository organizationRepository,
+        ISendOrganizationInvitesCommand sendOrganizationInvitesCommand,
+        ILogger<BulkResendOrganizationInvitesCommand> logger)
+    {
+        _organizationUserRepository = organizationUserRepository;
+        _organizationRepository = organizationRepository;
+        _sendOrganizationInvitesCommand = sendOrganizationInvitesCommand;
+        _logger = logger;
+    }
+
+    public async Task<IEnumerable<Tuple<OrganizationUser, string>>> BulkResendInvitesAsync(
+        Guid organizationId,
+        Guid? invitingUserId,
+        IEnumerable<Guid> organizationUsersId)
+    {
+        var orgUsers = await _organizationUserRepository.GetManyAsync(organizationUsersId);
+        _logger.LogUserInviteStateDiagnostics(orgUsers);
+
+        var org = await _organizationRepository.GetByIdAsync(organizationId);
+        if (org == null)
+        {
+            throw new NotFoundException();
+        }
+
+        var validUsers = new List<OrganizationUser>();
+        var result = new List<Tuple<OrganizationUser, string>>();
+
+        foreach (var orgUser in orgUsers)
+        {
+            if (orgUser.Status != OrganizationUserStatusType.Invited || orgUser.OrganizationId != organizationId)
+            {
+                result.Add(Tuple.Create(orgUser, "User invalid."));
+            }
+            else
+            {
+                validUsers.Add(orgUser);
+            }
+        }
+
+        if (validUsers.Any())
+        {
+            await _sendOrganizationInvitesCommand.SendInvitesAsync(
+                new SendInvitesRequest(validUsers, org));
+
+            result.AddRange(validUsers.Select(u => Tuple.Create(u, "")));
+        }
+
+        return result;
+    }
+}

src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/InviteUsers/IBulkResendOrganizationInvitesCommand.cs

@@ -0,0 +1,20 @@
+using Bit.Core.Entities;
+
+namespace Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.InviteUsers;
+
+public interface IBulkResendOrganizationInvitesCommand
+{
+    /// <summary>
+    /// Resend invites to multiple organization users in bulk.
+    /// </summary>
+    /// <param name="organizationId">The ID of the organization.</param>
+    /// <param name="invitingUserId">The ID of the user who is resending the invites.</param>
+    /// <param name="organizationUsersId">The IDs of the organization users to resend invites to.</param>
+    /// <returns>A tuple containing the OrganizationUser and an error message (empty string if successful)</returns>
+    Task<IEnumerable<Tuple<OrganizationUser, string>>> BulkResendInvitesAsync(
+        Guid organizationId,
+        Guid? invitingUserId,
+        IEnumerable<Guid> organizationUsersId);
+}
+
+