Add pilot version string to prom metrics (istio#10027)

* Add pilot version string to prom metrics

* Fix version string

* Move metric registration to init

pilot/pkg/bootstrap/server.go

@@ -36,6 +36,7 @@ import (
 	middleware "github.com/grpc-ecosystem/go-grpc-middleware"
 	prometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
 	"github.com/hashicorp/go-multierror"
+	prom "github.com/prometheus/client_golang/prometheus"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/keepalive"
@@ -119,6 +120,14 @@ func init() {
 	// get the grpc server wired up
 	// This should only be set before any RPCs are sent or received by this program.
 	grpc.EnableTracing = true
+
+	// Export pilot version as metric for fleet analytics.
+	pilotVersion := prom.NewGaugeVec(prom.GaugeOpts{
+		Name: "pilot_info",
+		Help: "Pilot version and build information.",
+	}, []string{"version"})
+	prom.MustRegister(pilotVersion)
+	pilotVersion.With(prom.Labels{"version": version.Info.String()}).Set(1)
 }
 
 // MeshArgs provide configuration options for the mesh. If ConfigFile is provided, an attempt will be made to