Add kuttl test artifacts to .gitignore

Simply ignore the `kubeconfig` and
`kuttl-report-openstack-lightspeed.xml` files that are generated during
a kuttl test run (eg: `make kuttl-test-ocp`).

Author: Akrog

.gitignore

@@ -26,3 +26,7 @@ go.work
 *.swp
 *.swo
 *~
+
+# Kuttl test files
+kubeconfig
+kuttl-report-openstack-lightspeed.xml