Add uhfHeaderId = MSDocsHeader-AspNet to docfx.json (#39)

Co-authored-by: Docs Allowlist Management <docs-allowlist-mgmt@microsoft.com>

docfx.json

@@ -85,6 +85,7 @@
     "overwrite": [],
     "externalReference": [],
     "globalMetadata": {
+      "uhfHeaderId": "MSDocsHeader-AspNet",
       "breadcrumb_path": "signalRbreadcrumb/toc.yml",
       "ms.author":"mimengis"
     },