builder beacon apis for gloas

[james-prysm]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

adds

• Support POST on /eth/v4/validator/blocks/{slot} with a BuilderConfig body and return the winning builder in the Eth-Builder-Url response header, per beacon-APIs #630.
• Add POST /eth/v1/validator/builder_preferences to forward per-builder preference entries to their builders.

The core logic is already there in grpc and this simply utilizes it, but needs to update protobuf for ssz.

there's also a few smaller issues on validation fixed

note: this pr does not hook up validator client to beacon node

Which issue(s) does this PR fix?

addresses ethereum/beacon-APIs#630

Other notes for review

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).

[syjn99]

func (s *Service) SubmitBuilderPreferences(ctx context.Context, entries []*ethpb.BuilderPreferencesEntry) []string {
	ctx, span := trace.StartSpan(ctx, "builder.SubmitBuilderPreferences")
	defer span.End()

	var (
		wg       sync.WaitGroup
		failures = make([]string, len(entries))
	)

	for i, e := range entries {
		if e == nil {
			continue
		}
		if len(e.GetUrl()) == 0 {
			log.Warn("Skipping builder preferences entry with no builder url")
			failures[i] = "builder url is required"
			continue
		}
		wg.Add(1)
		wg.Go(func() {
			url := string(e.Url)
			c, err := s.clientFor(url)
			if err == nil {
				req := &ethpb.BuilderPreferencesRequest{
					Preferences: &ethpb.BuilderPreferences{MaxExecutionPayment: e.MaxExecutionPayment},
					Auth:        e.Auth,
				}
				err = c.SubmitBuilderPreferences(ctx, bytesutil.ToBytes48(e.ProposerPubkey), req)
			}
			if err != nil {
				tracing.AnnotateError(span, err)
				log.WithError(err).WithField("builder", logs.MaskCredentialsLogging(url)).Warn("Could not submit builder preferences")
				failures[i] = "could not submit builder preferences: " + logs.MaskCredentialsLogging(err.Error())
			}
		})
	}
	wg.Wait()
	return failures
}

I don't think we need mutex here, as each entry owns its index so there's no concurrency issue. This looks much better to me, although it requires some changes at the caller side.

Also note that i and e can be safely used in goroutine as they are scoped in each iteration.

[james-prysm]

removed in here but i think the failures still need a map
5504a1e