Add pristine dotnet new webapi scaffold

Baseline commit of the untouched template so the M0 restructure lands as a
reviewable diff rather than appearing as the initial state.

Includes .gitignore and .gitattributes only; no source changes.

global.json

@@ -0,0 +1,7 @@
+{
+  "sdk": {
+    "version": "10.0.0",
+    "rollForward": "latestMinor",
+    "allowPrerelease": false
+  }
+}