feat(DefaultReadConfigQuery): add DefaultReadConfigQuery with caching and AutoMapper support

- Implemented DefaultReadConfigQuery and its handler for reading default configuration.
- Added memory caching using IMemoryCache to improve performance.
- Integrated AutoMapper to map Config entities to ConfigDto.
- Included extension method for easier MediatR query invocation.
- Added error handling for missing configuration records.

EnvelopeGenerator.Application/Configs/DefaultReadConfigQuery.cs

@@ -0,0 +1,87 @@
+using AutoMapper;
+using DigitalData.Core.Abstraction.Application.Repository;
+using DigitalData.Core.Exceptions;
+using EnvelopeGenerator.Application.Common.Dto;
+using EnvelopeGenerator.Domain.Entities;
+using MediatR;
+using Microsoft.Extensions.Caching.Memory;
+
+namespace EnvelopeGenerator.Application.Configs;
+
+/// <summary>
+/// 
+/// </summary>
+public class DefaultReadConfigQuery : IRequest<ConfigDto>
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    public static readonly Guid MemoryCacheKey = Guid.NewGuid();
+}
+
+/// <summary>
+/// 
+/// </summary>
+public static class DefaultReadConfigQueryExtensions
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="sender"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    public static Task<ConfigDto> ReadDefaultConfigAsync(this ISender sender, CancellationToken cancel = default) 
+        => sender.Send(new DefaultReadConfigQuery(), cancel);
+}
+
+/// <summary>
+/// 
+/// </summary>
+public class DefaultReadConfigQueryHandler : IRequestHandler<DefaultReadConfigQuery, ConfigDto>
+{
+    private readonly IRepository<Config> _repo;
+
+    private readonly IMapper _mapper;
+
+    private readonly IMemoryCache _cache;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="repo"></param>
+    /// <param name="mapper"></param>
+    /// <param name="cache"></param>
+    public DefaultReadConfigQueryHandler(IRepository<Config> repo, IMapper mapper, IMemoryCache cache)
+    {
+        _repo = repo;
+        _mapper = mapper;
+        _cache = cache;
+    }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="request"></param>
+    /// <param name="cancel"></param>
+    /// <returns></returns>
+    /// <exception cref="NotImplementedException"></exception>
+    public async Task<ConfigDto> Handle(DefaultReadConfigQuery request, CancellationToken cancel)
+    {
+        var config = await _cache.GetOrCreateAsync(DefaultReadConfigQuery.MemoryCacheKey, async entry =>
+        {
+            entry.AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(5);
+            var configs = await _repo.GetAllAsync(cancel);
+            var defaultConfig = configs.FirstOrDefault();
+            var defaultConfigDto = _mapper.Map<ConfigDto>(defaultConfig);
+            return defaultConfigDto;
+        });
+
+        if(config is null)
+        {
+            _cache.Remove(DefaultReadConfigQuery.MemoryCacheKey);
+            throw new NotFoundException("No configuration record is found.");
+        }
+
+        return config;
+    }
+}