Add .npmrc to prevent npmjs usage, even accidentally (#44986)

Author: marcpopMSFT

test/TestAssets/TestProjects/ProjectWithEsProjReference/.npmrc

@@ -0,0 +1,5 @@
+# this file is never used during the tests that test esproj support,
+# but is placed here to satisfy compliance rules for NPM usage.
+registry=https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public-npm/npm/registry/
+
+always-auth=true