Update receiver-ui-envelope route and add transforms

The `Path` matching rule for the `receiver-ui-envelope` route was updated to use `/envelope/{EnvelopeKey}` instead of the wildcard `/envelope/{**catch-all}` for more specific routing.

Additionally, a `Transforms` section was added to the route, which includes a transformation to set the path to `/index.html`.

EnvelopeGenerator.API/yarp.json

@@ -29,9 +29,12 @@
         "ClusterId": "receiver-ui",
         "Order": 100,
         "Match": {
-          "Path": "/envelope/{**catch-all}",
+          "Path": "/envelope/{EnvelopeKey}",
           "Methods": [ "GET", "HEAD" ]
-        }
+        },
+        "Transforms": [
+          { "PathSet": "/index.html" }
+        ]
       },
       "receiver-ui-static-assets": {
         "ClusterId": "receiver-ui",