Allow validators registration batching on Builder API /eth/v1/builder/validators (#13178)

* builder `NewClient`: Simplify + fix some typos.

* Validator client: Implement `validator-registration-batch-size` option

* Address Potuz comments

* Address Potuz's comments

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>
Co-authored-by: james-prysm <90280386+james-prysm@users.noreply.github.com>
Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

cmd/validator/flags/flags.go

@@ -346,7 +346,7 @@ var (
 		Name: "suggested-fee-recipient",
 		Usage: "Sets ALL validators' mapping to a suggested eth address to receive gas fees when proposing a block." +
 			" note that this is only a suggestion when integrating with a Builder API, which may choose to specify a different fee recipient as payment for the blocks it builds." +
-			" For additional setting overrides use the --" + ProposerSettingsFlag.Name + " or --" + ProposerSettingsURLFlag.Name + " Flags. ",
+			" For additional setting overrides use the --" + ProposerSettingsFlag.Name + " or --" + ProposerSettingsURLFlag.Name + " flags. ",
 		Value: params.BeaconConfig().EthBurnAddressHex,
 	}
 
@@ -364,6 +364,13 @@ var (
 		Usage: "Sets gas limit for the builder to use for constructing a payload for all the validators",
 		Value: fmt.Sprint(params.BeaconConfig().DefaultBuilderGasLimit),
 	}
+
+	// ValidatorRegistrationBatchSizeFlag sets the maximum size for one batch of validator registrations. Use a non-positive value to disable batching.
+	ValidatorRegistrationBatchSizeFlag = &cli.IntFlag{
+		Name:  "validator-registration-batch-size",
+		Usage: "Sets the maximum size for one batch of validator registrations. Use a non-positive value to disable batching.",
+		Value: 0,
+	}
 )
 
 // DefaultValidatorDir returns OS-specific default validator directory.

cmd/validator/main.go

@@ -79,6 +79,7 @@ var appFlags = []cli.Flag{
 	flags.ProposerSettingsFlag,
 	flags.EnableBuilderFlag,
 	flags.BuilderGasLimitFlag,
+	flags.ValidatorRegistrationBatchSizeFlag,
 	////////////////////
 	cmd.DisableMonitoringFlag,
 	cmd.MonitoringHostFlag,

cmd/validator/usage.go

@@ -113,6 +113,7 @@ var appHelpFlagGroups = []flagGroup{
 			flags.SuggestedFeeRecipientFlag,
 			flags.EnableBuilderFlag,
 			flags.BuilderGasLimitFlag,
+			flags.ValidatorRegistrationBatchSizeFlag,
 		},
 	},
 	{