Add custom authorization policies and minor Swagger fix

Introduce SenderOrReceiverFullyAuth and ReceiverFullyAuth policies for role-based authorization. Register these policies in Program.cs. Also, fix OpenApiReference type for Swagger security configuration.

EnvelopeGenerator.Domain/Constants/AuthorizationPolicies.cs

@@ -0,0 +1,8 @@
+namespace EnvelopeGenerator.Domain.Constants
+{
+    public static class AuthorizationPolicies
+    {
+        public const string SenderOrReceiverFullyAuth = "SenderOrReceiverFullyAuth";
+        public const string ReceiverFullyAuth = "ReceiverFullyAuth";
+    }
+}