Add securityContext to run as root for kaniko example 🤖

As of today, kaniko assumes it is running as root, which means, this
example fails on platform that default to run containers as random
uid (like OpenShift). Adding this securityContext make it explicit that
it needs to run as root.

Signed-off-by: Vincent Demeester <vdemeest@redhat.com>

Author: vdemeester

examples/taskruns/build-push-kaniko.yaml

@@ -55,6 +55,8 @@ spec:
     - --destination=$(outputs.resources.builtImage.url)
     - --context=$(inputs.params.pathToContext)
     - --oci-layout-path=$(inputs.resources.builtImage.path)
+    securityContext:
+      runAsUser: 0
   sidecars:
     - image: registry
       name: registry