Refactor email template query handling with MediatR

- Updated `ReadEmailTemplateQuery` to implement `IRequest<ReadEmailTemplateResponse?>`.
- Changed `ReadEmailTemplateResponse` from a record to a class with updated properties.
- Enhanced `EmailTemplateController` to inject `IEmailTemplateRepository` and `IMediator`, and made the `Get` method asynchronous.
- Introduced `ReadEmailTemplateMappingProfile` for AutoMapper mappings.
- Added `ReadEmailTemplateQueryHandler` to manage query logic and response mapping.

These changes improve the structure and maintainability of the email template querying process.

EnvelopeGenerator.GeneratorAPI/Controllers/EmailTemplateController.cs

@@ -5,6 +5,9 @@ using EnvelopeGenerator.Application.EmailTemplates.Commands.Reset;
 using EnvelopeGenerator.Application.EmailTemplates.Queries.Read;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using EnvelopeGenerator.Application.Contracts.Repositories;
+using EnvelopeGenerator.Application.DTOs;
+using MediatR;
 
 namespace EnvelopeGenerator.GeneratorAPI.Controllers;
 
@@ -17,17 +20,27 @@ namespace EnvelopeGenerator.GeneratorAPI.Controllers;
 [Authorize]
 public class EmailTemplateController : ControllerBase
 {
+    private readonly ILogger<EmailTemplateController> _logger;
+
     private readonly IMapper _mapper;
 
+    private readonly IEmailTemplateRepository _repository;
+
+    private readonly IMediator _mediator;
+
     /// <summary>
     /// Initialisiert eine neue Instanz der <see cref="EmailTemplateController"/>-Klasse.
     /// </summary>
     /// <param name="mapper">
+    /// <param name="repository">
     /// Die AutoMapper-Instanz, die zum Zuordnen von Objekten verwendet wird.
     /// </param>
-    public EmailTemplateController(IMapper mapper)
+    public EmailTemplateController(IMapper mapper, IEmailTemplateRepository repository, ILogger<EmailTemplateController> logger, IMediator mediator)
     {
         _mapper = mapper;
+        _repository = repository;
+        _logger = logger;
+        _mediator = mediator;
     }
 
     /// <summary>
@@ -45,10 +58,26 @@ public class EmailTemplateController : ControllerBase
     /// <response code="401">Wenn der Benutzer nicht authentifiziert ist.</response>
     /// <response code="404">Wenn die gesuchte Abfrage nicht gefunden wird.</response>
     [HttpGet]
-    public IActionResult Get([FromQuery] ReadEmailTemplateQuery? emailTemplate = null)
+    public async Task<IActionResult> Get([FromQuery] ReadEmailTemplateQuery? emailTemplate = null)
     {
-        // Implementation logic here
-        return Ok(); // Placeholder for actual implementation
+        try
+        {
+            if (emailTemplate is null || (emailTemplate.Id is null && emailTemplate.Type is null))
+            {
+                var temps = await _repository.ReadAllAsync();
+                return Ok(_mapper.Map<IEnumerable<EmailTemplateDto>>(temps));
+            }
+            else
+            {
+                var temp = await _mediator.Send(emailTemplate);
+                return temp is null ? NotFound() : Ok(temp);
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "{Message}", ex.Message);
+            return StatusCode(StatusCodes.Status500InternalServerError);
+        }
     }
 
     /// <summary>