Add .flow example to e2e tests

[nicolaferraro]

Similar to

camel-k/e2e/run_test.go

Lines 45 to 51 in 3a4c882

	t.Run("run xml", func(t *testing.T) {
	RegisterTestingT(t)
	Expect(kamel("run", "-n", ns, "files/xml.xml").Execute()).Should(BeNil())
	Eventually(integrationPodPhase(ns, "xml"), 5*time.Minute).Should(Equal(v1.PodRunning))
	Eventually(integrationLogs(ns, "xml"), 1*time.Minute).Should(ContainSubstring("Magicstring!"))
	Expect(kamel("delete", "--all", "-n", ns).Execute()).Should(BeNil())
	})

[lburgazzoli]

Depends on #781 as there's no more distinction between flow and yaml dsl