Builder ssz (#14976)

* wip

* refactoring functions for easier readability

* allow ssz for register validator

* changelog

* adding in blinded block submission tests

* adding in tests for header ssz

* fixing linting and tests

* adding in custom errors and fixing ssz validator registration

* Update api/client/builder/client.go

Co-authored-by: Manu NALEPA <enalepa@offchainlabs.com>

* Update api/client/builder/client.go

Co-authored-by: Manu NALEPA <enalepa@offchainlabs.com>

* manu's feedback

* linting

* adding in info log to notify that this setting was turned on

* fixing linting

* manu's feedback

* fixing import

---------

Co-authored-by: Manu NALEPA <enalepa@offchainlabs.com>

cmd/beacon-chain/flags/base.go

@@ -28,6 +28,14 @@ var (
 		Usage: "A MEV builder relay string http endpoint, this will be used to interact MEV builder network using API defined in: https://ethereum.github.io/builder-specs/#/Builder",
 		Value: "",
 	}
+
+	// EnableBuilderSSZ enables Builder APIs to send and receive in SSZ format
+	EnableBuilderSSZ = &cli.BoolFlag{
+		Name:    "enable-builder-ssz",
+		Aliases: []string{"builder-ssz"},
+		Usage:   "Enables Builder APIs to send and receive in SSZ format",
+	}
+
 	MaxBuilderConsecutiveMissedSlots = &cli.IntFlag{
 		Name:  "max-builder-consecutive-missed-slots",
 		Usage: "Number of consecutive skip slot to fallback from using relay/builder to local execution engine for block construction",