Add MassData API with CQRS, repository, and DbContext

Introduce MassData feature with new API endpoints for querying and upserting records by customer name. Add DTOs, AutoMapper profile, MediatR CQRS handlers, repository pattern, and MassDataDbContext. Register new services in DI and add MassDataConnection to configuration. Upsert uses stored procedure. Enables full CRUD for Massdata via dedicated API.

DbFirst.Application/MassData/Queries/GetAllMassDataHandler.cs

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+using AutoMapper;
+using DbFirst.Application.Repositories;
+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public class GetAllMassDataHandler : IRequestHandler<GetAllMassDataQuery, List<MassDataReadDto>>
+{
+    private readonly IMassDataRepository _repository;
+    private readonly IMapper _mapper;
+
+    public GetAllMassDataHandler(IMassDataRepository repository, IMapper mapper)
+    {
+        _repository = repository;
+        _mapper = mapper;
+    }
+
+    public async Task<List<MassDataReadDto>> Handle(GetAllMassDataQuery request, CancellationToken cancellationToken)
+    {
+        var items = await _repository.GetAllAsync(request.Skip, request.Take, cancellationToken);
+        return _mapper.Map<List<MassDataReadDto>>(items);
+    }
+}

DbFirst.Application/MassData/Queries/GetAllMassDataQuery.cs

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+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public record GetAllMassDataQuery(int? Skip, int? Take) : IRequest<List<MassDataReadDto>>;

DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameHandler.cs

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+using AutoMapper;
+using DbFirst.Application.Repositories;
+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public class GetMassDataByCustomerNameHandler : IRequestHandler<GetMassDataByCustomerNameQuery, MassDataReadDto?>
+{
+    private readonly IMassDataRepository _repository;
+    private readonly IMapper _mapper;
+
+    public GetMassDataByCustomerNameHandler(IMassDataRepository repository, IMapper mapper)
+    {
+        _repository = repository;
+        _mapper = mapper;
+    }
+
+    public async Task<MassDataReadDto?> Handle(GetMassDataByCustomerNameQuery request, CancellationToken cancellationToken)
+    {
+        var item = await _repository.GetByCustomerNameAsync(request.CustomerName, cancellationToken);
+        return item == null ? null : _mapper.Map<MassDataReadDto>(item);
+    }
+}

DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameQuery.cs

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+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public record GetMassDataByCustomerNameQuery(string CustomerName) : IRequest<MassDataReadDto?>;