Introduce luci-go components version metric.

appengine/tsmon/standardmetrics.go

Index: appengine/tsmon/standardmetrics.go
diff --git a/appengine/tsmon/standardmetrics.go b/appengine/tsmon/standardmetrics.go
index 54432b14d0dda632c29c0d8008a527779f268c55..b5c3a3c4d24d7b4fa2de26a4238b754a3468ae2f 100644
--- a/appengine/tsmon/standardmetrics.go
+++ b/appengine/tsmon/standardmetrics.go
@@ -12,6 +12,7 @@ import (
 	"github.com/luci/luci-go/common/tsmon"
 	"github.com/luci/luci-go/common/tsmon/metric"
 	"github.com/luci/luci-go/common/tsmon/runtimestats"
+	"github.com/luci/luci-go/common/tsmon/versions"
 )
 
 var (
@@ -40,6 +41,7 @@ func collectGlobalMetrics(c context.Context) {
 //
 // It is called by each individual process right before flushing the metrics.
 func collectProcessMetrics(c context.Context, s *tsmonSettings) {
+	versions.Report(c)
 	if s.ReportRuntimeStats {
 		runtimestats.Report(c)
 	}