Add /eth/v2/validator/aggregate_attestation (#14481)

* add endpoint

* changelog

* fix tests

* fix endpoint

* remove useless broken code

* review + fix endpoint

* gaz

* fix aggregate selection proof test

* fixes

* new way of aggregating

* nit

* fix part of the tests

* fix tests

* cleanup

* fix AggSelectionProof test

* tests

* v1 tests

* v2 tests

* commiittee bits

---------

Co-authored-by: rkapka <radoslaw.kapka@gmail.com>
Co-authored-by: Radosław Kapka <rkapka@wp.pl>

api/server/structs/endpoints_validator.go

@@ -7,7 +7,8 @@ import (
 )
 
 type AggregateAttestationResponse struct {
-	Data *Attestation `json:"data"`
+	Version string          `json:"version,omitempty"`
+	Data    json.RawMessage `json:"data"`
 }
 
 type SubmitContributionAndProofsRequest struct {