Fixed all relationship and write errors in all entities

PyroFetes/Models/ServiceProvider.cs

@@ -0,0 +1,13 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace PyroFetes.Models;
+
+public class ServiceProvider
+{
+    [Key] public int Id { get; set; } 
+    [Required] public decimal Price { get; set; }
+    
+    //Relations
+    public int ProviderTypeId { get; set; }
+    public ProviderType? ProviderType { get; set; }
+}