Refactor authentication and enhance logging

Updated `Authorize` attributes in multiple controllers to use
`AuthenticationSchemes = AuthScheme.Sender` instead of
`Policy = AuthPolicy.Sender`, reflecting a shift in the
authentication mechanism.

Added detailed logging in `EnvelopeReceiverController` to handle
cases where stored procedures return `OUT_SUCCESS=false`,
providing contextual information for debugging.

Removed unused SQL code and declarations in
`EnvelopeReceiverController` to improve code readability and
maintainability.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Controllers/DocumentController.cs

@@ -30,7 +30,7 @@ public class DocumentController(IMediator mediator, IAuthorizationService authSe
     /// <param name="query">Encoded envelope key.</param>
     /// <param name="cancel">Cancellation token.</param>
     [HttpGet]
-    [Authorize(Policy = AuthPolicy.Sender)]
+    [Authorize(AuthenticationSchemes = AuthScheme.Sender)]
     public async Task<IActionResult> GetDocument(CancellationToken cancel, [FromQuery] ReadDocumentQuery? query = null)
     {
         if (query is null)