feat(kubectl): respect a few global $WERF_* env vars

Make "werf kubectl" respect $WERF_KUBE_CONFIG, $WERF_KUBECONFIG, $WERF_KUBE_CONTEXT, $WERF_SKIP_TLS_VERIFY_REGISTRY.

Signed-off-by: Ilya Lesikov <ilya@lesikov.com>

cmd/werf/kubectl/kubectl.go

@@ -1,11 +1,42 @@
 package kubectl
 
 import (
+	"fmt"
+	"os"
+
 	"github.com/spf13/cobra"
 	"k8s.io/kubectl/pkg/cmd"
+	"k8s.io/kubectl/pkg/cmd/util"
+
+	"github.com/werf/werf/cmd/werf/common"
 )
 
 func NewCmd() *cobra.Command {
-	kubectlRootCmd := cmd.NewDefaultKubectlCommand()
-	return kubectlRootCmd
+	kubectlCmd := cmd.NewDefaultKubectlCommand()
+
+	kubeConfigFlag := kubectlCmd.Flag("kubeconfig")
+	kubeConfigFlag.Usage = "Path to the kubeconfig file to use for CLI requests (default $WERF_KUBE_CONFIG, or $WERF_KUBECONFIG, or $KUBECONFIG)"
+	if kubeConfigEnvVar := common.GetFirstExistingKubeConfigEnvVar(); kubeConfigEnvVar != "" {
+		if err := os.Setenv("KUBECONFIG", kubeConfigEnvVar); err != nil {
+			util.CheckErr(fmt.Errorf("unable to set $KUBECONFIG env var: %w", err))
+		}
+	}
+
+	kubeContextFlag := kubectlCmd.Flag("context")
+	kubeContextFlag.Usage = "The name of the kubeconfig context to use (default $WERF_KUBE_CONTEXT)"
+	if werfKubeContextEnvVar := os.Getenv("WERF_KUBE_CONTEXT"); werfKubeContextEnvVar != "" {
+		if err := kubectlCmd.Flags().Set("context", werfKubeContextEnvVar); err != nil {
+			util.CheckErr(fmt.Errorf("unable to set context flag for kubectl: %w", err))
+		}
+	}
+
+	skipTlsVerifyRegistryFlag := kubectlCmd.Flag("insecure-skip-tls-verify")
+	skipTlsVerifyRegistryFlag.Usage = "If true, the server's certificate will not be checked for validity. This will make your HTTPS connections insecure (default $WERF_SKIP_TLS_VERIFY_REGISTRY)"
+	if isSkipTlsVerifyRegistry := common.GetBoolEnvironmentDefaultFalse("WERF_SKIP_TLS_VERIFY_REGISTRY"); isSkipTlsVerifyRegistry {
+		if err := kubectlCmd.Flags().Set("insecure-skip-tls-verify", "true"); err != nil {
+			util.CheckErr(fmt.Errorf("unable to set insecure-skip-tls-verify flag for kubectl: %w", err))
+		}
+	}
+
+	return kubectlCmd
 }