Add whoami as a second real app (docs/08 hands-on exercise)

apps/whoami/namespace.yaml

@@ -0,0 +1,10 @@
+# A Namespace is a way to group related resources together inside the
+# cluster, like a folder. Keeping "whoami" separate from other apps lets you
+# manage, view, and delete them independently (e.g. `kubectl -n whoami get pods`).
+#
+# We create this explicitly, as its own file, rather than letting Argo CD
+# invent it implicitly. That way it shows up in Git like everything else.
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: whoami