Enhance EnvelopeReceiver queries and controller

- Updated `EnvelopeReceiverQuery` to include an optional, nullable `Status` parameter.
- Modified `ReadEnvelopeReceiverQuery` to inherit from the updated `EnvelopeReceiverQuery`.
- Added new using directives in `EnvelopeReceiverController` and enhanced response documentation to include a 401 Unauthorized response.
- Implemented authorization for the `GetEnvelopeReceiver` method.
- Improved documentation and method signature for `GetReceiverName` to accept a `ReadReceiverNameQuery` object.
- Introduced a new `ReadReceiverNameQuery` record for querying the last used salutation of a receiver.

EnvelopeGenerator.Application/EnvelopeReceivers/EnvelopeReceiverQuery.cs

@@ -3,9 +3,7 @@
 namespace EnvelopeGenerator.Application.EnvelopeReceivers;
 
 /// <summary>
-/// Stellt eine Abfrage zum Lesen eines Envelope-Empfängers dar.
+/// Stellt eine Abfrage für einen Envelope-Empfänger dar.
 /// </summary>
-/// <param name="MinStatus"></param>
-/// <param name="MaxStatus"></param>
-/// <param name="IgnoreStatus"></param>
-public record EnvelopeReceiverQuery(StatusQuery Status);
+/// <param name="Status">Der Status der Abfrage, optional.</param>
+public record EnvelopeReceiverQuery(StatusQuery? Status = null);