enhance(k8s): reach Kubernetes services by their id when it is a DNS subdomain (#1320)

On Kubernetes a service is reached by its id made a DNS label, so some service ids might become unreachable. For example, the `devstoreaccount1.azurite.local` service of Gitea's [MSSQL tests](https://github.com/go-gitea/gitea/blob/2fe74d3cdd5184a7e22e32e47772caa78d077489/.github/workflows/pull-db-tests.yml#L229) is only in the pod's hosts as `devstoreaccount1-azurite-local`, while the tests connect to the id as written. Container names must be DNS labels, but `hostAliases` accepts DNS subdomains, so an id that is one is now added there too, and to `no_proxy`, as on Docker where a service is reached by its id.

The warning for a service not reachable by its id now also covers ids that differ only in case, as Kubernetes hostnames are lowercase.

---------

Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1320
Reviewed-by: Lunny Xiao <[email protected]>
Reviewed-by: bircni <[email protected]>
Reviewed-by: silverwind <[email protected]>
Co-authored-by: Zettat123 <[email protected]>

act/container/kubernetes_test.go

@@ -129,6 +129,19 @@ func serveLocalExec(t *testing.T, w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func TestKubernetesServiceHostnames(t *testing.T) {
+	for id, hostnames := range map[string][]string{
+		"db":                             {"db"},
+		"My_DB":                          {"my-db"},
+		"devstoreaccount1.azurite.local": {"devstoreaccount1-azurite-local", "devstoreaccount1.azurite.local"},
+		"DB.Local":                       {"db-local", "db.local"},
+		strings.Repeat("a", 64):          {strings.Repeat("a", 63), strings.Repeat("a", 64)},
+		strings.Repeat("a", 254):         {strings.Repeat("a", 63)},
+	} {
+		assert.Equal(t, hostnames, KubernetesServiceHostnames(id), id)
+	}
+}
+
 func TestKubernetesPodRunsJobThroughAPI(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("uses POSIX shell")