feat(api): Hinzufügen des EnvelopeControllers mit GetCurrentAsync-Methode zur Umschlagabfrage

- Implementierung des `EnvelopeController` in der Route `api/envelope` mit der Methode `GetCurrentAsync`, um Umschläge basierend auf der Benutzer-ID abzurufen.
- Fehlerbehandlung hinzugefügt, wenn die Benutzer-ID keine Ganzzahl ist, mit einem möglichen Problem bei der Erstellung der Claims-Liste.

EnvelopeGenerator.GeneratorAPI/Controllers/EnvelopeController.cs

@@ -0,0 +1,50 @@
+using DigitalData.Core.DTO;
+using EnvelopeGenerator.Application.Contracts;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace EnvelopeGenerator.GeneratorAPI.Controllers
+{
+    [Route("api/[controller]")]
+    [ApiController]
+    [Authorize]
+    public class EnvelopeController : ControllerBase
+    {
+        private ILogger<EnvelopeController> _logger;
+        private readonly IEnvelopeService _envelopeService;
+
+        public EnvelopeController(ILogger<EnvelopeController> logger, IEnvelopeService envelopeService)
+        {
+            _logger = logger;
+            _envelopeService = envelopeService;
+        }
+
+        [Authorize]
+        public async Task<IActionResult> GetCurrentAsync(bool current_user)
+        {
+            try
+            {
+                var id = this.GetId();
+
+                if (id is int intId)
+                    return await _envelopeService.ReadByIdAsync(intId).ThenAsync(
+                        Success: Ok,
+                        Fail: IActionResult (msg, ntc) =>
+                        {
+                            _logger.LogNotice(ntc);
+                            return StatusCode(StatusCodes.Status500InternalServerError);
+                        });
+                else
+                {
+                    _logger.LogError("Despite successful authorization, the 'api/envelope' route encountered an issue: the user ID is not recognized as an integer. This may be due to the removal of the ID during the creation of the claims list.");
+                    return StatusCode(StatusCodes.Status500InternalServerError);
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "{Message}", ex.Message);
+                return StatusCode(StatusCodes.Status500InternalServerError);
+            }
+        }
+    }
+}

EnvelopeGenerator.GeneratorAPI/Controllers/ReceiverController.cs

@@ -17,8 +17,6 @@ namespace EnvelopeGenerator.GeneratorAPI.Controllers
         {
         }
 
-
-
         [HttpGet]
         public async Task<IActionResult> Get([FromQuery] string? emailAddress = null, [FromQuery] string? signature = null)
         {