metrics, cmd/geth: informational metrics (prometheus, influxdb, opentsb) (#24877)

This chang creates a GaugeInfo metrics type for registering informational (textual) metrics, e.g. geth version number. It also improves the testing for backend-exporters, and uses a shared subpackage in 'internal' to provide sample datasets and ordered registry. 

Implements #21783

---------

Co-authored-by: Martin Holst Swende <martin@swende.se>

cmd/geth/config.go

@@ -22,10 +22,10 @@ import (
 	"fmt"
 	"os"
 	"reflect"
+	"runtime"
+	"strings"
 	"unicode"
 
-	"github.com/urfave/cli/v2"
-
 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/accounts/external"
 	"github.com/ethereum/go-ethereum/accounts/keystore"
@@ -43,6 +43,7 @@ import (
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/naoina/toml"
+	"github.com/urfave/cli/v2"
 )
 
 var (
@@ -177,6 +178,20 @@ func makeFullNode(ctx *cli.Context) (*node.Node, ethapi.Backend) {
 	}
 	backend, eth := utils.RegisterEthService(stack, &cfg.Eth)
 
+	// Create gauge with geth system and build information
+	if eth != nil { // The 'eth' backend may be nil in light mode
+		var protos []string
+		for _, p := range eth.Protocols() {
+			protos = append(protos, fmt.Sprintf("%v/%d", p.Name, p.Version))
+		}
+		metrics.NewRegisteredGaugeInfo("geth/info", nil).Update(metrics.GaugeInfoValue{
+			"arch":          runtime.GOARCH,
+			"os":            runtime.GOOS,
+			"version":       cfg.Node.Version,
+			"eth_protocols": strings.Join(protos, ","),
+		})
+	}
+
 	// Configure log filter RPC API.
 	filterSystem := utils.RegisterFilterAPI(stack, backend, &cfg.Eth)