feat: created register method for entry

JOBot.Backend/DAL/Context/AppDbContext.cs

@@ -8,4 +8,12 @@ class AppDbContext : DbContext
     public DbSet<User> Users { get; set; }
 
     public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {   
+        base.OnModelCreating(modelBuilder);
+
+        modelBuilder.Entity<User>()
+            .HasAlternateKey(b => b.TelegramId);
+    }
 }