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.
Introduced AuthProxyDocumentFilter to programmatically document the POST /api/auth proxy login endpoint in Swagger. The filter defines request body schemas, example values, query parameter, and response codes. Registered the filter in Program.cs for OpenAPI generation.
