feat: add a group command

Application/Cqrs/Group/Commands/UpdateGroup/UpdateGroupCommand.cs

@@ -0,0 +1,9 @@
+using MediatR;
+
+namespace Mirea.Api.DataAccess.Application.Cqrs.Group.Commands.UpdateGroup;
+
+public class UpdateGroupCommand : IRequest
+{
+    public required int Id { get; set; }
+    public required int FacultyId { get; set; }
+}

Application/Cqrs/Group/Commands/UpdateGroup/UpdateGroupCommandHandler.cs

@@ -0,0 +1,20 @@
+using MediatR;
+using Microsoft.EntityFrameworkCore;
+using Mirea.Api.DataAccess.Application.Common.Exceptions;
+using Mirea.Api.DataAccess.Application.Interfaces.DbContexts.Schedule;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Mirea.Api.DataAccess.Application.Cqrs.Group.Commands.UpdateGroup;
+
+public class UpdateGroupCommandHandler(IGroupDbContext dbContext) : IRequestHandler<UpdateGroupCommand>
+{
+    public async Task Handle(UpdateGroupCommand request, CancellationToken cancellationToken)
+    {
+        var entity = await dbContext.Groups.FirstOrDefaultAsync(g => g.Id == request.Id, cancellationToken: cancellationToken) ?? throw new NotFoundException(typeof(Domain.Schedule.Group), nameof(Domain.Schedule.Group.Id), request.Id);
+
+        entity.FacultyId = request.FacultyId;
+
+        await dbContext.SaveChangesAsync(cancellationToken);
+    }
+}