Account for state availability when fetching sync committees #7115
Description
Short placeholder issue (will add more later):
Lighthouse currently loads the state from the start of the sync committee period when sync duties are requested. This can cause confusion when that state is not available, but a state from the same period is available. We could use the state_upper_limit to bound the slot of the state fetched, something like: max(sync_committee_start_slot, state_upper_limit) (if state_upper_limit != INT_MAX).