Add new email template types and query records

- Updated `Constants.vb` to include new email template types:
  `DocumentRejected_ADM`, `DocumentRejected_REC`, and
  `DocumentRejected_REC_2`.

- Introduced `EmailTemplateQuery` record in `EmailTemplateQuery.cs`
  with parameters for `Id`, `Type`, and `Culture`, along with
  German documentation.

- Added `ReadEmailTemplateQuery` record in
  `ReadEmailTemplateQuery.cs` that inherits from
  `EmailTemplateQuery` for reading email templates.

EnvelopeGenerator.Application/EmailTemplates/Query/Read/ReadEmailTemplateQuery.cs

@@ -0,0 +1,10 @@
+namespace EnvelopeGenerator.Application.EmailTemplates.Query.Read;
+
+
+/// <summary>
+/// Stellt eine Abfrage dar, um eine E-Mail-Vorlage zu lesen.
+/// Diese Klasse erbt von <see cref="EmailTemplateQuery"/>.
+/// </summary>
+public record ReadEmailTemplateQuery : EmailTemplateQuery
+{
+}