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.API/Controllers/MassDataController.cs

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+using DbFirst.Application.MassData;
+using DbFirst.Application.MassData.Commands;
+using DbFirst.Application.MassData.Queries;
+using MediatR;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DbFirst.API.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class MassDataController : ControllerBase
+{
+    private readonly IMediator _mediator;
+
+    public MassDataController(IMediator mediator)
+    {
+        _mediator = mediator;
+    }
+
+    [HttpGet]
+    public async Task<ActionResult<IEnumerable<MassDataReadDto>>> GetAll([FromQuery] int? skip, [FromQuery] int? take, CancellationToken cancellationToken)
+    {
+        var resolvedTake = take is null or <= 0 ? 200 : take;
+        var result = await _mediator.Send(new GetAllMassDataQuery(skip, resolvedTake), cancellationToken);
+        return Ok(result);
+    }
+
+    [HttpGet("{customerName}")]
+    public async Task<ActionResult<MassDataReadDto>> GetByCustomerName(string customerName, CancellationToken cancellationToken)
+    {
+        var result = await _mediator.Send(new GetMassDataByCustomerNameQuery(customerName), cancellationToken);
+        if (result == null)
+        {
+            return NotFound();
+        }
+
+        return Ok(result);
+    }
+
+    [HttpPost("upsert")]
+    public async Task<ActionResult<MassDataReadDto>> Upsert(MassDataWriteDto dto, CancellationToken cancellationToken)
+    {
+        var result = await _mediator.Send(new UpsertMassDataByCustomerNameCommand(dto), cancellationToken);
+        return Ok(result);
+    }
+}