Add memory caching support in HistoryController

- Updated `EnvelopeGenerator.Extensions.csproj` to include
  `Microsoft.Extensions.Caching.Memory` package.
- Refactored `HistoryController` to use `IMemoryCache` for
  caching functionality.
- Replaced manual dictionary creation in `GetReferenceTypes`
  with a call to `GetEnumAsDictionary<ReferenceType>()`.
- Changed enum type in `GetEnvelopeStatus` to
  `ReferenceType` for consistency.
- Introduced `MemoryCacheExtensions` class with
  `GetEnumAsDictionary<TEnum>` method for efficient enum
  to dictionary conversion.

EnvelopeGenerator.GeneratorAPI/Controllers/HistoryController.cs

@@ -1,8 +1,9 @@
-using DigitalData.EmailProfilerDispatcher.Abstraction.Entities;
-using EnvelopeGenerator.Application.Contracts.Services;
+using EnvelopeGenerator.Application.Contracts.Services;
 using EnvelopeGenerator.Application.Histories.Queries.Read;
+using EnvelopeGenerator.Extensions;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Caching.Memory;
 using static EnvelopeGenerator.Common.Constants;
 
 
@@ -20,15 +21,18 @@ public class HistoryController : ControllerBase
 
     private readonly IEnvelopeHistoryService _service;
 
+    private readonly IMemoryCache _memoryCache;
+
     /// <summary>
     /// Konstruktor für den HistoryController.
     /// </summary>
     /// <param name="logger">Der Logger, der für das Protokollieren von Informationen verwendet wird.</param>
     /// <param name="service">Der Dienst, der für die Verarbeitung der Umschlaghistorie verantwortlich ist.</param>
-    public HistoryController(ILogger<HistoryController> logger, IEnvelopeHistoryService service)
+    public HistoryController(ILogger<HistoryController> logger, IEnvelopeHistoryService service, IMemoryCache memoryCache)
     {
         _logger = logger;
         _service = service;
+        _memoryCache = memoryCache;
     }
 
     /// <summary>
@@ -49,17 +53,7 @@ public class HistoryController : ControllerBase
     [Authorize]
     public IActionResult GetReferenceTypes()
     {
-        // Enum zu Schlüssel-Wert-Paar
-        var referenceTypes = Enum.GetValues(typeof(ReferenceType))
-                                 .Cast<ReferenceType>()
-                                 .ToDictionary(rt =>
-                                 {
-                                     var key = rt.ToString();
-                                     var keyAsCamelCase = char.ToLower(key[0]) + key[1..];
-                                     return keyAsCamelCase;
-                                 }, rt => (int)rt);
-
-        return Ok(referenceTypes);
+        return Ok(_memoryCache.GetEnumAsDictionary<ReferenceType>());
     }
 
     /// <summary>
@@ -105,8 +99,8 @@ public class HistoryController : ControllerBase
     public IActionResult GetEnvelopeStatus([FromQuery] ReferenceType? related = null)
     {
         // Enum zu Schlüssel-Wert-Paar
-        var referenceTypes = Enum.GetValues(typeof(EnvelopeStatus))
-                                 .Cast<EnvelopeStatus>()
+        var referenceTypes = Enum.GetValues(typeof(ReferenceType))
+                                 .Cast<ReferenceType>()
                                  .ToDictionary(rt =>
                                  {
                                      var key = rt.ToString();