Changes in sync committee gossip rules

[tbenr]

We should check ethereum/consensus-specs#4015 validate it and apply eventual changes

[rolfyone]

added a note about some wording on the consensus-specs change, but overall seems sensible - may mean another queue.

[etan-status]

They asked for approvals in the spec PR, anyone mind revisiting the spec PR so that we can finally get this closed? it's been 1.5 years xD

[rolfyone]

Im very cautious to accept anything else until ePBS is done honestly.