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>

core/blockchain.go

@@ -60,6 +60,8 @@ var (
 	headFinalizedBlockGauge = metrics.NewRegisteredGauge("chain/head/finalized", nil)
 	headSafeBlockGauge      = metrics.NewRegisteredGauge("chain/head/safe", nil)
 
+	chainInfoGauge = metrics.NewRegisteredGaugeInfo("chain/info", nil)
+
 	accountReadTimer   = metrics.NewRegisteredTimer("chain/account/reads", nil)
 	accountHashTimer   = metrics.NewRegisteredTimer("chain/account/hashes", nil)
 	accountUpdateTimer = metrics.NewRegisteredTimer("chain/account/updates", nil)
@@ -322,6 +324,9 @@ func NewBlockChain(db ethdb.Database, cacheConfig *CacheConfig, genesis *Genesis
 	bc.currentFinalBlock.Store(nil)
 	bc.currentSafeBlock.Store(nil)
 
+	// Update chain info data metrics
+	chainInfoGauge.Update(metrics.GaugeInfoValue{"chain_id": bc.chainConfig.ChainID.String()})
+
 	// If Geth is initialized with an external ancient store, re-initialize the
 	// missing chain indexes and chain flags. This procedure can survive crash
 	// and can be resumed in next restart since chain flags are updated in last step.