Add envelope-receiver login endpoint support

Added `AddEnvelopeReceiverLoginOperation` to `AuthProxyDocumentFilter` to define a new Swagger operation for the `/api/Auth/envelope-receiver/{key}` endpoint. Introduced the `EnvelopeReceiverLogin` record for the request body. Updated `yarp.json` to configure routing for the new endpoint, ensuring the `cookie` query parameter is always set to `true`. Modified `Apply` to include the new operation in Swagger documentation.

EnvelopeGenerator.API/yarp.json

@@ -10,6 +10,17 @@
         "Transforms": [
           { "PathSet": "/api/auth/sign-flow" }
         ]
+      },
+      "auth-envelope-receiver-login": {
+        "ClusterId": "auth-hub",
+        "Match": {
+          "Path": "/api/Auth/envelope-receiver/{key}",
+          "Methods": [ "POST" ]
+        },
+        "Transforms": [
+          { "PathPattern": "/api/auth/envelope-receiver/{key}" },
+          { "QueryValueParameter": "cookie", "Set": "true" }
+        ]
       }
     },
     "Clusters": {