refactor(EnvelopeController): migrate envelope update to MediatR with annotations

- Renamed `Update` action to `CreateOrUpdate`.
- Replaced manual signing logic with `_mediator.SignDocAsync`.
- Added `ExpandoObject` parameter to handle document annotations.
- Improved authorization checks and logging for missing claims.
- Kept legacy `Reject` endpoint intact with obsolete services.

EnvelopeGenerator.Web/wwwroot/js/network.js

@@ -15,8 +15,8 @@
      * @param {any} documentId
      * @param {any} json
      */
-    async postEnvelope(envelopeKey, documentId, json) {
-        return this.postRequest(`/api/envelope/${envelopeKey}?index=${documentId}`, json)
+    async postEnvelope(documentId, json) {
+        return this.postRequest(`/api/envelope?index=${documentId}`, json)
             .then(this.wrapJsonResponse.bind(this))
     }