adding ssz for get block endpoint (#15390)

* adding get ssz

* adding some tests

* gaz

* adding ssz to e2e

* wip ssz

* adding in additional check on header type

* remove unused

* renaming json rest handler, and adding in usage of use ssz debug flag

* fixing unit tests

* fixing tests

* gaz

* radek feedback

* Update config/features/config.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update config/features/flags.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update config/features/flags.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/get_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/get_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/get_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* addressing feedback

* missing import

* another missing import

* fixing tests

* gaz

* removing unused

* gaz

* more radek feedback

* fixing context

* adding in check for non accepted conent type

* reverting to not create more edgecases

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

proto/prysm/v1alpha1/beacon_block.go

@@ -5,6 +5,12 @@ import (
 	enginev1 "github.com/OffchainLabs/prysm/v6/proto/engine/v1"
 )
 
+// GenericConverter defines any struct that can be converted to a generic beacon block.
+// We assume all your versioned block structs implement this method.
+type GenericConverter interface {
+	ToGeneric() (*GenericBeaconBlock, error)
+}
+
 // ----------------------------------------------------------------------------
 // Phase 0
 // ----------------------------------------------------------------------------