Add CloseWorkflowCommand with MediatR support

Introduce CloseWorkflowCommand and CloseWorkflowResult records
in CloseWorkflowCommand.cs within the DigitalData.TaskFlow
namespace. The command encapsulates data for closing a workflow,
including WisagId, Source, ProcessId, ClosingMethodId, Comment,
and RejectionReasonId. The result record provides ResultCode and
ResultMessage to convey the operation's outcome. These changes
utilize MediatR, aligning with the CQRS pattern for state
modification.

src/core/DigitalData.TaskFlow.Application/Features/Workflows/Commands/CloseWorkflowCommand.cs

@@ -0,0 +1,15 @@
+using MediatR;
+
+namespace DigitalData.TaskFlow.Application.Features.Workflows.Commands;
+
+public sealed record CloseWorkflowCommand(
+    int WisagId,
+    string Source,
+    long ProcessId,
+    int ClosingMethodId,
+    string? Comment,
+    byte? RejectionReasonId) : IRequest<CloseWorkflowResult>;
+
+public sealed record CloseWorkflowResult(
+    int ResultCode,
+    string ResultMessage);