Update SurveyLib and add Excel export functionality

SurveyBackend/SurveyBackend.API/Controllers/ExportController.cs

@@ -0,0 +1,26 @@
+using Microsoft.AspNetCore.Mvc;
+using SurveyLib.Tools.Tools;
+
+namespace SurveyBackend.Controllers;
+
+[ApiController]
+[Route("api/export")]
+public class ExportController
+{
+    private readonly TableExporter _tableExporter;
+
+    public ExportController(TableExporter tableExporter)
+    {
+        _tableExporter = tableExporter;
+    }
+
+    [HttpGet("excel/{surveyId:int}")]
+    public async Task<IActionResult> ExportSurveyById(int surveyId)
+    {
+        var fileBytes = await _tableExporter.ExportDataBySurveyIdAsync(surveyId);
+        return new FileContentResult(fileBytes, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
+        {
+            FileDownloadName = $"survey_{surveyId}_{DateTime.UtcNow:yyyyMMdd_HHmmss}.xlsx"
+        };
+    }
+}