feat(kumactl) add install loki for log aggregation

Add the Loki stack to `kumactl install` allowing to see logs
directly in Grafana. The yaml for loki was inspired by:
`https://grafana.github.io/loki/charts`

* Add a new install command to kubectl:
  `kubectl install logging`
* Upgrate Grafana version to 7.0.3 that accepts loki as a
  data source.

app/kumactl/cmd/install/install.go

@@ -17,5 +17,6 @@ func NewInstallCmd(pctx *kumactl_cmd.RootContext) *cobra.Command {
 	cmd.AddCommand(newInstallMetrics())
 	cmd.AddCommand(newInstallTracing())
 	cmd.AddCommand(newInstallDNS())
+	cmd.AddCommand(newInstallLogging())
 	return cmd
 }

app/kumactl/cmd/install/install_logging.go

@@ -0,0 +1,53 @@
+package install
+
+import (
+	"github.com/Kong/kuma/app/kumactl/pkg/install/data"
+	"github.com/Kong/kuma/app/kumactl/pkg/install/k8s"
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+
+	"github.com/Kong/kuma/app/kumactl/pkg/install/k8s/logging"
+)
+
+type loggingTemplateArgs struct {
+	Namespace string
+}
+
+func newInstallLogging() *cobra.Command {
+	args := struct {
+		Namespace string
+	}{
+		Namespace: "kuma-logging",
+	}
+	cmd := &cobra.Command{
+		Use:   "logging",
+		Short: "Install Logging backend in Kubernetes cluster (Loki)",
+		Long:  `Install Logging backend in Kubernetes cluster (Loki) in a 'kuma-logging' namespace`,
+		RunE: func(cmd *cobra.Command, _ []string) error {
+			templateArgs := loggingTemplateArgs{
+				Namespace: args.Namespace,
+			}
+
+			templateFiles, err := data.ReadFiles(logging.Templates)
+			if err != nil {
+				return errors.Wrap(err, "Failed to read template files")
+			}
+
+			renderedFiles, err := renderFiles(templateFiles, templateArgs, simpleTemplateRenderer)
+			if err != nil {
+				return errors.Wrap(err, "Failed to render template files")
+			}
+
+			sortedResources := k8s.SortResourcesByKind(renderedFiles)
+
+			singleFile := data.JoinYAML(sortedResources)
+
+			if _, err := cmd.OutOrStdout().Write(singleFile.Data); err != nil {
+				return errors.Wrap(err, "Failed to output rendered resources")
+			}
+			return nil
+		},
+	}
+	cmd.Flags().StringVar(&args.Namespace, "namespace", args.Namespace, "namespace to install logging to")
+	return cmd
+}