fix file upload

Tsi1.Api/Tsi1.Api/Controllers/SectionItemController.cs

Tsi1.Api/Tsi1.Api/Startup.cs

Tsi1.Api/Tsi1.BusinessLayer/Dtos/SectionItemCreateDto.cs

Tsi1.Api/Tsi1.BusinessLayer/Dtos/SectionItemTypeDto.cs

Tsi1.Api/Tsi1.BusinessLayer/Helpers/ErrorMessages.cs

Tsi1.Api/Tsi1.BusinessLayer/Helpers/MappingProfile.cs

.../Tsi1.BusinessLayer/Interfaces/ISectionItemTypeService.cs

Tsi1.Api/Tsi1.BusinessLayer/Services/FileService.cs

...Api/Tsi1.BusinessLayer/Services/SectionItemTypeService.cs

Tsi1.Api/Tsi1.DataLayer/Entities/File.cs

Tsi1.Api/Tsi1.DataLayer/Entities/Forum.cs

.../Tsi1.DataLayer/EntityConfiguration/ForumConfiguration.cs

...r/Migrations/20201107181002_fix-section-items.Designer.cs

....DataLayer/Migrations/20201107181002_fix-section-items.cs

...Api/Tsi1.DataLayer/Migrations/Tsi1ContextModelSnapshot.cs