remove "experimental" from backfill flag name (#15690)

* remove "experimental" from backfill flag name

* backwards-compatible alias

* changelog

---------

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>

beacon-chain/sync/backfill/service.go

@@ -22,7 +22,7 @@ import (
 
 type Service struct {
 	ctx             context.Context
-	enabled         bool // service is disabled by default while feature is experimental
+	enabled         bool // service is disabled by default
 	clock           *startup.Clock
 	store           *Store
 	ms              minimumSlotter

changelog/kasey_rename-backfill-flag.md

@@ -0,0 +1,2 @@
+### Changed
+- Renamed the `--enable-experimental-backfill` flag to `--enable-backfill` to signal that it is more mature.

cmd/beacon-chain/sync/backfill/flags/flags.go

@@ -11,9 +11,9 @@ var (
 	// EnableExperimentalBackfill enables backfill for checkpoint synced nodes.
 	// This flag will be removed once backfill is enabled by default.
 	EnableExperimentalBackfill = &cli.BoolFlag{
-		Name: "enable-experimental-backfill",
-		Usage: "Backfill is still experimental at this time. " +
-			"It will only be enabled if this flag is specified and the node was started using checkpoint sync.",
+		Name:    "enable-backfill",
+		Aliases: []string{"enable-experimental-backfill"},
+		Usage:   "Backfill will only be enabled when this flag is specified on a node using checkpoint sync.",
 	}
 	// BackfillBatchSize allows users to tune block backfill request sizes to maximize network utilization
 	// at the cost of higher memory.