Add prepare-all-payloads flag (#12260)

* Add prepare-all-payloads flag

* add unit tests

* do not use the nsc

---------

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

config/features/config.go

@@ -65,6 +65,8 @@ type Flags struct {
 	EnableVerboseSigVerification bool // EnableVerboseSigVerification specifies whether to verify individual signature if batch verification fails
 	EnableOptionalEngineMethods  bool // EnableOptionalEngineMethods specifies whether to activate capella specific engine methods
 
+	PrepareAllPayloads bool // PrepareAllPayloads informs the engine to prepare a block on every slot.
+
 	// KeystoreImportDebounceInterval specifies the time duration the validator waits to reload new keys if they have
 	// changed on disk. This feature is for advanced use cases only.
 	KeystoreImportDebounceInterval time.Duration
@@ -206,6 +208,10 @@ func ConfigureBeaconChain(ctx *cli.Context) error {
 		logEnabled(enableOptionalEngineMethods)
 		cfg.EnableOptionalEngineMethods = true
 	}
+	if ctx.IsSet(prepareAllPayloads.Name) {
+		logEnabled(prepareAllPayloads)
+		cfg.PrepareAllPayloads = true
+	}
 	Init(cfg)
 	return nil
 }

config/features/flags.go

@@ -114,6 +114,10 @@ var (
 		Name:  "enable-optional-engine-methods",
 		Usage: "Enables the optional engine methods",
 	}
+	prepareAllPayloads = &cli.BoolFlag{
+		Name:  "prepare-all-payloads",
+		Usage: "Informs the engine to prepare all local payloads. Useful for relayers and builders",
+	}
 )
 
 // devModeFlags holds list of flags that are set when development mode is on.
@@ -159,6 +163,7 @@ var BeaconChainFlags = append(deprecatedBeaconFlags, append(deprecatedFlags, []c
 	enableFullSSZDataLogging,
 	enableVerboseSigVerification,
 	enableOptionalEngineMethods,
+	prepareAllPayloads,
 }...)...)
 
 // E2EBeaconChainFlags contains a list of the beacon chain feature flags to be tested in E2E.